PicoLisp is written in C, or the 64-bit version in assembler. It is Posix-dependent, so you need to run it in Cygwin for Windows, although somebody is working on a platform independent version based upon Midipix to eliminate the Posix dependency [2].
The creator of PicoLisp, Alex Burger, created it for his own use decades ago. It has a built-in database and Prolog interpreter. It is very fast for an interpreted Lisp, and there are lots of examples on rosettacode.org.
It is fexprs-based instead of sexprs as far as I know.
I like it a lot, but since I am on Windows for my livecoding / game dev hobby, I have not gone too far with it. I am hoping the Midipix work takes off. I also run Linux on my notebook, but all of my work nowadays is on Windows. .NET Core might change that.
Most games still run on Windows, and the ones on Linux have compatibility issues across the various Linux distros.
There may be a glowing white Apple on most web-dev's notebooks, but my 3 year old Alienware plays games with a Technicolor LED show that would put the F&F film franchise to shame ;)