This subject is probably outside the scope of this forum. It could be done but it is not simple and the methods would be different for any system you use.
If I were to do this, there would be a couple of methods I would look at…
1. Amember is a membership purchase system which integrates with EE. The system has an EE plugin which shuttles information back and forth. You would probably have to create a plugin for the Clipshare application. There is a pretty good thread on Amember located [url=http://ellislab.com/forums/viewthread/63226/[/url].
2. In the above case, Amember basically works as a bridge. Information gets shuttled back and forth and Amember acts as the central repository for handling members. You could create your own bridge which would act much the same.
3. Modification to the applications themselves. This could get really tricky. People here would love you if you could build an OpenID module into EE but you would probably have to do the same for Clipshare if the app does not already support it. I believe the Joomla communities have hacked Wordpress and 3rd party forum scripts as add-ons to Joomla and perhaps you could do the same thing but this process would be beyond the scope of this forum.
4. You could check out CodeIgniter and build a basic CMS which is built around Clipshare to add the features you like but still integrate with the system. CodeIgniter might be more malleable for your purposes than EE because it is designed to be light weight and get out of your way.
You probably need to pick a method that would be best for you and then start asking more specific questions in the developer forums because this is a big subject.
My 2 cents, there are probably other options.