He's spending 16 days on each language: Smalltalk, FP, Ada, Python, OCaml, BrainF*, i86 assembly, Prolog, Erlang, Forth, D, Lazy K, Haskell, FORTRAN, Lua, and Scheme.

Everything he writes is in a subversion repository: http://16languages.googlecode.com/svn/

More information on the format: http://16languages.blogspot.com/2007/09/rules.html