The quick2wire-cpp-api is a port of the quick2wire-python-api written entirely in C++ with C support. It grants access to the GPIO ports to unprivileged users using the quick2wire gpio-admin tool (or a modified version in Arch Linux).
The library is a literal port of its parent project, so users of the Python implementation should feel comfortable with this variant as well.
This is a work in progress. So far, only the GPIO is implemented (and only the OUT mode), but a port of the whole API is on the way.