In line with its work for the Department of Homeland Security, boosting the security of open soruce code, Coverity has put a database of 2,500 projects online, describing the application architecture of each.
Designs like the one at the right, for the Apache Web server, are clickable and deep. Wherever you see a plus sign, you can click on the live diagram for deeper information, right down to the code level.
You can find open source projects either by category or by name.
Developers writing plug-ins can use this information to be certain their work aligns with that of the project. Or they can study the architecture of existing open soruce projects for hints on how to build larger systems.
This is a great, free development resource. I don't expect a long talkback thread here but if you do develop open source software yourself, check it out.