Deliverance is a great library that lets you easily re-theme external websites on the fly. Designed as WSGI middleware, it can be easily combined with some proxying to integrate a bunch of websites together
You can use deliverance plus proxying out-of-the-box using the deliverance-proxy command. However, I was interested in using Deliverance as middleware from code. This turned out to be none too trivial to do – all the examples on the internet seemed to focus on using deliverance-proxy or using it in an ini file.
I should also mention the following sources which were all of help in my quest: