Muds, mushes, etc - About every six months, I start a new one from scratch. Eventually I'll actually finish one :) My most recent used perl as the scripting language and overdosed on the Safe module. I'm still sorta sad I never finished it.
Simple scripting languages - Designed for very very specialized things. For example, I wrote this weird test harness language that turned out to be very similar to what make uses.
Simple templating systems - Again, really specialized. My most recent helps me convert some D&D text files into HTML. (this is the result). They automate class tables and such.
Re: "Rites of Passage" wheel reinventing