Unison suffers from the Lisp Curse - it's written in OCaml, a similarly powerful but small-audience language. It "just works", so there doesn't need to be much activity.
Absolutely, I have a entry in my journal about wanting to rewrite Unison in C. Never got around to it, but it would still be fun. The same goes with Wings 3D, cool app, but Erlang? Really?
oof. I think we've gotten much different takeaways from The Lisp Curse.
Maybe, I really like Lisp and especially Scheme. Don't get me wrong. I just think that a lot of projects suffer from being written in a language with a small community or even, at the time of conception, a thriving yet fleeting community (Perl, Ruby, etc).
Unison seems to be maintained, there just isn't much to maintain. Perhaps being in C would attract a huge community to make up for the increased work required, or perhaps that wouldn't be sustainable and we're better off with projects that can better "hibernate".
Not C but not super powerful seems like the worst of both worlds.
Unison and Wings 3D are both projects I wanted to make changes to when I was using them. Downloaded the source code for both, spent a day or so reading and fiddling and got bored. I actually like learning new languages, but I don’t have the capacity to learn a new language, build system, tooling, style & formatting, install the right Emacs mode, and so on just to scratch a little itch.
The problem is that it didn't just work e.g. on Windows with filenames that contained non-Ascii chars for a long time.