Based on Gambit-C: A scheme to C (or javascript... and I think there may be other targets) compiler. Comes with a Scheme->target compiler, then compile that code, and deploy. So, you write in Scheme, and deliver in C...

Comes with an interpreter. Supports macros, etc. and Gambit supports easy C FFI, option for infix syntax, massive threading, full numeric tower

Easy to hack on (in my opinion), and performs very well. Gambit-C has been my "goto" Scheme for the past decade.

Could be used as an "extension language", but not its main purpose. Mostly, a way to deliver Scheme code that runs fast.

Racket has a better IDE -- but I like the simplicity of Gambit-C.

Supports r7rs, networking, leveldb, lmdb, mysql, and is very fast.