Plugin Based Application

Hi to all.

I am developing an application, i want it to be totally modular and
plugin based.

E.g. The main application would have a Core plugin, on which every
thing works, and further as needed new features, i would develop new
plugins and upload.Like redmine..

Can any one help me or provide any good reference material on it.

I will greatly be thankful.

Regards
Nazar