brent Not quite like Superfrog, but more like Super Mario, there is Supertux (included in the Solus repository). Has the advantage of being fully open-source. Not quite as fast as Superfrog though.
For what it's worth I just tried Superfrog HD on Linux with Steam Proton and it worked fine (had to disable Vsync though, otherwise it ran on ludicrous speed).
But since you don't like Steam that isn't an option. 😉
