C, Perl, Python, Java and LISP — the dominant languages in open-source development. This list has changed over time, but slowly. Java bumped C++(HAR HAR) off of it, and Python appears to be recruiting people who would otherwise gravitate to LISP(HAR HAR) (which used to be much more important than it is now). Smalltalk and Prolog are also popular in small but influential communities.