Chicken - A portable and efficient cross-platform Scheme implementation that compiles to C.
JavaScript - Lightweight, interpreted, object-oriented language with first-class functions
RxJS - Reactive Extensions for Javascript
Allegro - Allegro 4 and Allegro 5 are cross-platform, libraries mainly aimed at video game and multimedia...
Gambit - Cross-platform chess game.
Qt - Powerful, flexible and easy to use, Qt will help you not only meet your tight deadline, but also reduce the maintainable code by an astonishing percentage.