FlightCrew is a C++, cross-platform, native code epub validator. It is composed of three parts:

• FlightCrew, the validation library
• FlightCrew-cli, the command-line front-end to the FlightCrew library
• FlightCrew-gui, the GUI front-end to the FlightCrew library

FlightCrew runs on Windows, Linux and Mac OS X (and possibly other platforms). FlightCrew-gui uses the Qt Framework, but the rest does not. The validation library has no external dependencies outside of those included in the source tree and built along with FlightCrew.
Since FlightCrew is licensed under LGPLv3, it can be directly used by closed-source projects as well as open-source ones. It was initially created for Sigil, the epub editor.
Work on FlightCrew was inspired by the inadequacies of other epub checkers.

Operating systems: Windows, Linux, Mac OSX
Screen libraries: Qt for GUI