One of the things that we've been doing recently is playing string quartets with some friends. We're currently working on Mozart's "Hunt" quartet and an arrangement of Corelli's Christmas concerto for quartet. It may be unseasonal, but it's still lovely.
A serendipitous discovery just before we started rehearsals a few months ago was the
Mutopia project, a collection of free (as in both beer and speech) sheet music, transcribed from editions on which the copyright has expired. Printouts aren't as nice to play from as a properly bound edition (they have a habit of falling off the music stand at page turns, even when sellotaped together[1]), but you can't argue with the value for money.
It's all typeset using
Lilypond, a program comparable to LaTeX. There is some flavour of TeX which can do music, but from what I remember (having played with it once, some time ago), it's a bit fiddly. Lilypond is quite nice - bashing the notes in takes a little while (and unfortunately isn't directly compatible with
abc, the other ASCII standard for music, although that's nothing that a few lines of your favourite scripting language couldn't sort out) but once that stage is done, it's remarkably easy to produce pdfs of scores. It does all the things you'd expect, such as jiggling the notes around if you tell it that you want a part for a transposing intstrument.
[1] Or scotched together, as they say here. Fie, I say. Everyone knows that Scotch is liquid, and no use at all for holding things together. In fact, it's rather counterproductive - I certainly have problems holding myself together following too much Scotch.