I would like to make a suggestion to enhance the page returned for file not found errors (404). The 3D effect on the picture is quite nice, by the way.
Consider this page, for example:
Recently, the file was renamed cuviddec.c, hence the 404. It would be nice if the returned page included useful links. In this example, that would be:
https://github.com/FFmpeg/ (the owner dashboard)
https://github.com/FFmpeg/FFmpeg/ (the corresponding repository)
https://github.com/FFmpeg/FFmpeg/commits/master/libavcodec/cuvid.c (the history of the file, valid even after the file was renamed)
This would help people who arrived there following an obsolete link from outside to find their way back to something useful.
Expressed as a set of rules, it would be:
If $request_path matches the regexp ^/([^/]+)/ then add a link to /$1/.
If $request_path matches the regexp ^/([^/]+)/([^/]+)/ then add a link to /$1/$2/.
If $request_path matches the regexp ^/([^/]+)/([^/]+)/blob/(.*) then add a link to /$1/$2/commits/$3.
Note that this could be done purely on client side. In fact, once I am done with this mail I will endeavour to write a greasemonkey script or bookmarklet to do just that. But I think it would be more convenient for visitors to have it by default.