It's becoming rare and we, digital archeologists have to dig further and further. Where has all the code gone?
Anyway, a few unrotting bits:
Regular Expressions
- pregexp: https://ds26gte.github.io/pregexp/index.html (Dorai Sitaram)
- irregex: http://synthcode.com/scheme/irregex/ (Alex Shinn)
Prolog
- schelog: https://ds26gte.github.io/schelog/index.html (Dorai Sitaram, again)
Symbolic Algebra
- scmutils: https://groups.csail.mit.edu/mac/users/gjs/6946/ (Sussman, Abelson, ...)