The first part is for people who want support hacking the buildsystem of their own projects. Not sure of the best way to migrate to extra-cmake-modules as part of your shift to KF5? Getting “deprecated” or other CMake warnings you want to resolve? Can you think of something really useful the buildsystem could do in your project, but you don’t know how to do it? Come along, and I (and hopefully others) will be there to give you a hand. Likewise, if you feel comfortable writing stuff in CMake, and you want to help other developers, come along to lend a hand – you don’t need to be an expert!
The second part is for people who want to contribute to extra-cmake-modules. If you have some CMake code in your project you think other projects will find useful, or you have ideas for improvements in the existing modules, come along and pitch in.