KlayGE is a cross-platform open source game engine with plugin-based architecture. It's started since 2003. The explicit goal of KlayGE is: to arm your engine with cutting-edge technology. It provides a framework to make game development, testing, porting as simple as possible.
Before compiling KlayGE, Python 2.7+ and CMake 3.4+ must be installed first. Then you can run build_all.py to build KlayGE, its Samples, Tools, etc. For details, please see http://www.klayge.org/wiki/index.php/Installation.
KlayGE can be developed on those platforms, with no limitation.
KlayGE can be deployed and run on those runtime platforms. Some of them doesn't supports all plugins. Details in http://www.klayge.org/wiki/index.php/Platforms
As an open source project, KlayGE benefits greatly from both the volunteer work of helpful developers and good bug reports made by users.
If you've noticed a bug or have an idea that you'd like to see come real, why not work on it? Bug reports and feature requests are typically submitted to the issue tracker https://github.com/gongminmin/KlayGE/issues.
If you want contribute some code, please check http://www.klayge.org/wiki/index.php/Workflow_of_contributing_code before submitting a patch or pull request.