Can I Call It...?
"Can I Call It...?" is a Javascript-based utility for checking if the name you'd like for your new, shiny project has already been used by somebody else.
It uses project data from Github, Ruby Gems, PyPI, Maven, Debian and Fedora. (Only Github repositories with >5 watchers (stars) are considered 'significant' enough to worry about.)
It was written by Ian Renton. Source code is available under the BSD licence.
I just want to use it!
That's OK! There's a version running at cici.onlydreaming.net.