I want to apply for GSOC this year. Since Guile has recently obtained a compilation/language framework, I was thinking that an implementation of the Lua language for Guile, under the auspices of the GNU Project, would be a good fit.
A little background on Lua: It has a reputation as an "extensible, embeddable" programming language. It inherits a lot from Scheme, including closures and tail call optimization, but unfortunately not macros :( I would say it definitely meets the criteria of "ubiquitous intelligent language for extension." It's probably the most popular "extension language" out there. At maybe ~10000 lines of C code, it's not an unreasonable summer project either. Personally, I am interested in learning more about parsing and compilation. I'd also like to brush up on my Scheme. Moreover, I think the addition of Lua, similarly to Emacs Lisp, would put Guile in a better position to subvert existing applications that use Lua as their scripting language (a lot!). Let me know what you think.