This isn't really advertised all that loudly. But SmartGit is free for personal use now:
SmartGit – Git Client for Windows, macOS, Linux
I've only been using it a little bit so far, but from the bit I've seen it seems to be a lot more functional than SourceTree.
I imagine that things like VSCode having pretty passable in-built version control and extensions is probably putting some pressure on these kinds of products.