Everything? The full projects are in lisp syntax (s-expressions), not Algol-like syntax (C-like syntax) that most people are familiar with. Personally I mostly use Clojure, but lots of lisp-like languages offer the same (simpler) experience of programming.

probably the best use of s-expressions is as an alternative to json which you can implement in 50 lines of code

e.g. pretty good for config files or basic serialization