... or the shoemaker's children go barefoot?
I would like to fix some styling & have an idea for the feature (and a lot of free time) but I cannot find any github.com page on github.com.
GitHub isn't open-source, but you can apply your ideas on an (open-source) GitHub-look-alike:
A ruby application with its source code here).
They accept suggestions and pull requests
Update 2015: you also have other GitHub-look-alike in Go: