also Sussman's propagators are nice to check out [0]

[0] The Art of the Propagator (mit url down for the moment)

Great list of languages that don't fit the conventional families. I've been curious about some of them, like Petri nets and term rewriting, and will enjoy exploring the others.

Found a working link to the paper about propagators.

The Art of the Propagator, Alexey Radul and Gerald Jay Sussman. https://groups.csail.mit.edu/mac/users/gjs/6.945/readings/ar... (PDF)