I’m working on a Content Management Framework with this basic functionality that you are asking for. Basically you will install it and you will have a foundation to built your project on top of it.
Nice part is that, even the foundation is simple with few features, it will allow you to install and manage extensions, themes and language packs. It uses a hooking system just like wordpress so you can define hooks and later attach to them.
It proven to be solid since i have a few apps built on top of it, the changes i am doing now are design related.
However, i am not 100% done with it and documentation is missing at this point.
In case you are interested, i can try to hurry up the development and get a working version on codecanyon in maybe a week (will have to check if it complies with the rules here too).