Suggest CodeIgniter CMS for webapp
PyroCMS has been around for a long time and is tried and tested. The documentation is growing here and the Plugin, Tag, Module and Widget architecture mean you can do anything you like.
http://pyrocms.com/documentation/
You can download extra modules from our recently launched Add-on area to see how they work:
I love pyro and developing module is also easy in pyro if you are codeigniter developer. But for multilingual and html 5 backend i am using ionize cms. In short no one is perfect in this world. You have to choose according to your requirements.