CHICKEN has a more permissive license, larger community (and therefore more libraries) and a slightly better bus factor than Gambit and Gerbil. Gambit is faste

CHICKEN has a more permissive license, larger community (and therefore more libraries) and a slightly better bus factor than Gambit and Gerbil. Gambit is faster on many benchmarks and has multiple backends. This makes it easier to run inside a browser, for example, with the JS backend. It also has better introspective capabilities than CHICKEN, if I remember correctly. I believe Gambit is currently R5RS only with no plans to implement R7RS, and it has no native module system like CHICKEN does. If I understand correctly, Gerbil adds this to Gambit, but there's also the Black Hole module system. I don't know how compatible those are. Both have full continuations, tail call optimization and take the standard serious. You can compile stand-alone programs with both, and both can link to C libraries quite easily. Full disclosure: I'm a CHICKEN developer and my knowledge of Gambit is somewhat limited.