The features of a useful writing procrastination project are that it produces something of long-term utility, and that it has a natural end.
The work I've been recently doing on my genealogy fits, since the information I can pull from records about my family tree (assuming a judicious pruning of remote cousins and in-laws) is finite. You can read about that here.
The second project is larger, but even more finite. You see, I have this website of Scandinavian fiddle tunes…
Blue Rose Music
Twenty-five years ago, in my 30s, I was listening to some Swedish twin-fiddle records (of which I already had a few dozen — now many hundreds). As a harmony singer I've always been a sucker for two- and three-fiddle folk music performances, and the best of these come from the Swedish folk tradition.
I said to myself, “Boy, I like this stuff. Gee, I wish I could do that.” And then the light bulb went off — how hard could it be? I had a musical background and knew my way around a piano and a guitar (as an amateur).
So, I picked up a violin for the first time, just to play the Scandinavian folk repertoire, and never looked back.

You can read about this in some detail here, but the short version is I've been going to workshops and playing solo and with small bands now for a very long time, primarily for the use of dance groups who are equally fond of the folk dance traditions of Sweden and Norway.
Playing for dances in pick-up groups means you carry around huge binders of material because the repertoire demand for all the dance forms is very large in the Scandinavian genres. It's not like, say, Irish, where if you know jigs, slip-jigs, reels, waltzes, and polkas, you're covered for most dance requests. No, the tune categories alone are broad, and many of those categories cover several different dance types with different musical requirements.
I improved the situation by using early digital music printing programs to create binders of incipits, the first bars of each part of the tune, to serve as quick hints for what tune to play next for dancers. Then, naturally, I put up a website, Blue Rose, where those lists of incipits went online, with links to PDF files for each tune, so that people who played together regularly could find them. When I went to workshops, I posted the tunes we learned for everyone to use.
Over time, this grew…
There are now 2000 Scandinavian fiddle tunes in my binders and up on Blue Rose.