Free Music Scores
Nowadays, there's so much in this category that it seems almost foolish to list any, but the ones below have been particularly useful to me.
Choral Public Domain Library — Free choral music
IMSLP — If you're a musician and don't know about this site already, I'm sad for you. It's worth becoming a member, and surely not just because the 15-second download delay is removed for members.
Mutopia Project — Free sheet music for everyone. Available scores have been made with the Lilypond notation program.
Music Notation
The learning curve of any notation software is quite massive and most people, unsurprisingly, will stick to the one they know even if isn't ultimately "the best" (whatever that means) for their purposes. Obviously, what's easy or intuitive to one person won't be the same of another, and all these programs—and a host of others not listed here—approach engraving music in different ways, sometimes radically so. However, the ones below have very active, ardent communities surrounding them through forums, mailing lists, Facebook groups/pages, etc. Patience and a lot of time is required for learning any of them.
In the end, a quote from Marie Barone (from one of my favorite TV sitcoms, Everybody Loves Raymond) says it best: “Vacuum cleaners don't clean houses; people clean houses.” So, I say, ”Notation programs don't engrave music; people engrave music.” Theoretically, then, almost any notation program can get one 95% or so of the way, at least for the most typical use cases, but it's up to the engraver to know their craft— to know and employ good rules of notation, and to have the kind of eye and judgment necessary in making their scores imminently readable and useful. I mean, who really wants to read and play from a crappy-looking score? (Speaking of crappy-looking scores, I'm re-engraving many pieces on my site which could stand to use a facelift, particularly the ones involving instrumental ensembles. Learning to be a good engraver is a process, and one's judgment changes as one ages—and when one's eyesight requires more adequately-sized print!)
Lilypond — This is my favorite notation software, even if this admission puts me in a decided minority. First of all, it's completely free, but it's in constant, active development by a host of very intelligent folk. This does not use a graphical interface (i.e., where one can move a note or text around with a mouse); rather, it uses text input. While a very different approach than all the programs listed here, the resulting scores are, I believe, stunningly beautiful, and my frustration/annoyance level is typically quite low compared to using any other notation program. I've been using LilyPond in some capacity since 2006 (mostly melody-only versions of hymns for our church leaflets), but, since 2016, have embraced it more fully for all my engraving needs. Typically, I can engrave music in LilyPond substantially faster than in any graphical program. If you’re curious, view the Lilypond code I once used for Wondrous Love, intro #6 (I've changed/refined my templates over the years).
Frescobaldi — Not a notation program, but I include it because it's a text editor front-end for LilyPond that has templates, and uses color-coded syntax. Frescobaldi is the best and easiest way to create scores with LilyPond.
MuseScore — Useful, free, ever-evolving music notation program for macOS, Windows, and Linux. Perhaps a little easier program to learn/use than many. It keeps getting better with every update, though I typically only use it once or twice a year just to see their progress. If your needs are modest, this is a good way to go. If you need really advanced features and granular control, probably look elsewhere.
Sibelius — Most of the music on this site made before 2016 was engraved using (much older versions of) Sibelius. Most of my brass and string arrangements were engraved with Sibelius, but I've started using Lilypond for most new ones. Since Avid bought out Sibelius, my enthusiasm for the software has waned significantly, even if still a viable option for many. Though I don't use Sibelius as regularly as I once did, I will admit that my fluency and speed in using it surprisingly remains about the same as when it was my primary program, and I even remember most of the keyboard shortcuts. It has a companion tablet app, but, at this writing, I haven't tried it.
Dorico — The most recent music notation program to come on the scene. Very powerful (and expensive). But, if you want the best and greatest notation software that has a graphical interface, I highly recommend it. Why do I feel it's better than most? They've been in an unusual position of being able to build something new from scratch, using a very different paradigm than Finale or Sibelius. There's a companion app for the iPad which is very good. I have purchased this for use at my church, and do use it from time to time.
Finale — If this is the kind of music notation app you like, then you're sure getting a good one. That said, I wish my Finale friends well; more than likely they continue to use it because it's what they know, and that is perfectly understandable. Indeed, it's a very powerful program which offers extreme granularity in control, but, to my mind, it takes too much effort to get great-looking scores by default ... kind of like cleaning a house with a toothbrush—possible, yet ill-advised. But, it still enjoys many faithful users, so to each their own.
Ear Training/Theory
Ricci Adams' musictheory.net — Impressive, free ear/theory training which can be done in a browser; also has a link to an older version of the site, where the lessons and exercises can be downloaded and run on a Mac, Windows or Linux computer. The equivalent app for tablets/phones is called Tenuto and is available on iOS or Android. One of its most useful features is the ability to setup very specific exercises in advance (limiting range, difficulty, scope, etc.) which then has its own unique URL (web link). This means that I can prepare, in advance, a webpage with the appropriate exercise links for the students' varying levels of ability. This can save a massive amount of time, especially when working simultaneously with multiple students of various ages and progress.
Other (music-related)
GoodNotes app (iOS & macOS) — though not specifically music-related, this is the app I use for writing all my music. I use a staff paper template (one comes with the app, but I made a custom one for my needs). One can have any number of "notebooks" in the app. I'm currently on page 865 of one of my notebooks ... it has a search facility that can recognize (legible) handwriting and the Apple Pencil support/interface is better than in any other app I've used. There are a ton of other impressive features, most of which I don't need on a regular basis, but some of them can come in handy for special projects & meetings.
Aria Maestosa — A great MIDI editor/sequencer. After a visual proofreading of my scores, they all get proofread by me playing their MIDI file, auto-generated by LilyPond at the same time a score is produced.
Audacity — free sound editor and recorder. When this wasn't available for Mac following an operating system upgrade, I switched to Reaper. It is now once again available for the Mac, but I love Reaper too much to go back.
Fission — an audio editor that looks great and is useful, particularly when one want to trim an .mp3 or normalize it
ForScore (iOS & macOS) — the premier music-reading app.
Hauptwerk — The world of digitally-sampled organs. Many of the recordings on this site were recorded by me using the Friesach organ sample set, an instrument brought to life virtually by the extremely talented Piotr Grabowski. In my opinion, this is one of the best instruments available for Hauptwerk. I would hope that anyone listening to the organ mp3s on this site would agree that its clarity and overall sound are convincing and exciting to hear.
Ravenscroft 275 — The world of digitally-sampled pianos. If one is to believe the advertising hype—and in this case, I do—this instrument is a “virtual instrument like no other.” Indeed, it can make any crappy, electronic keyboard sound like a million dollars (well, perhaps at least $500,000).
I feel a clarification is in order here. As a professional musician, I, of course, prefer “real” instruments. However, here’s what is also very real—the hassle and time it takes to set up recording equipment under favorable conditions (the instruments are in tune and good-working order; street and heating/air-conditioning and other noises are mitigated; interruptions are minimized). While there are downsides to recording virtually, particularly with the piano, the ease and comfort with which it can be accomplished makes it the obvious choice for showcasing the music available on this site. In the end, it's still me playing, but having almost no setup and not having to worry about ambient noise ruining recordings is a pretty big deal—and a quite lovely luxury—especially given the limited time I have with all the various hats I wear.
Reaper — a cheap DAW (Digital Audio Workstation, $60), similar to Audacity, but much more powerful and full-featured. I use Reaper for almost all of my audio editing.
Staff paper generator — Very cool web-based way to generate staff paper of all sizes, instrumentation, etc.
Other (non-music)
Claris FileMaker — This is possibly my favorite piece of software of all time. This relational database program is what's really powering this website, even if it isn't doing so directly. All of my pieces are catalogued in a specially-designed (by me) database; all of that info gets exported from FileMaker and then imported into this website using a marvelous plugin, Tablepress Pro. I can make add or correct any database info and, in less than a minute, have my site be brought up-to-date.
FileMaker also generates the relevant information (into a plain text file) used to make the various books available on this site. With a LaTeX file template I've created for each book genre, using the TeXShop software, I've created templates for the various book genres, complete with a framework which includes provisions for a cover page, table of contents, and page-numbering. That plain text file is fed into the appropriate template where it is read and parsed, ultimately creating a compilation of PDFs into one giant PDF. Using LaTeX commands in the code, I've programmed FileMaker to make the necessary calculations ensuring that 2-page pieces are always positioned on the left & right, thus eliminating page turns, and auto-inserting the note about "this page is intentionally left blank" if it's necessary to include.
Keyboard Maestro — This is one of the first things that gets installed on any new computer of mine. It is automation software for the Mac and I use it extensively every day. It saves me gobs of time.
Nitro PDF Pro — A great alternative to using Adobe Acrobat. This allows for editing of PDFs (adding/correcting text, etc.), doing OCR (optical character recognition of scanned documents), deskewing of scanned docs that are crooked, and redacting, to name a few of its useful features.
SortMyList — A cool utility to transform text in various ways
Time Calculator — A useful way to add up times (like when preparing a recital program that's supposed to have a certain amount of music)
Transmit — Software for transferring all the music files to my website (an FTP program).
Wordsplay — Online Boggle-like game; very addicting!