My 2012 fork of groovy/groovy-core — the Git repository for the Groovy programming language itself, from the Codehaus era. I forked it back when I was working heavily in the Groovy/JVM ecosystem and wanted to follow (and poke at) the language source directly.
This one is pure history now. The upstream README itself notes the repository is no longer used: Groovy moved to the Apache Software Foundation, and current development happens in the apache/groovy mirror, which is also where pull requests go today.
I keep the fork as a snapshot of that era — Groovy powered a lot of my work at the time (see my Griffon plugin fork from the same period), and having the compiler and standard library source one git grep away was how I learned my way around a serious JVM codebase.
Language: Java
Source code: github.com/avnit/groovy-core Upstream: github.com/groovy/groovy-core (superseded by apache/groovy)