JSI: small JavaScript interpreter in pure C suitable for embedding
jsish.sourceforge.net
jsish.sourceforge.net
http://samsung.github.io/jerryscript/
It is truly tiny:
* Can work in less than 64kB RAM
* Doesn't need a full-blown operating system because necessary runtime components (such as libc functions) are provided by JerryScript itself
I ran into some issues when trying to use clojurescript with it though.
For many. many years I used spidermonkey from mozilla (and it's descendants), but it's no longer small at all, the footprint is pretty big nowadays.