What practices do you have while developing and maintaining projects of this size?
There are many school of thoughts for managing large software projects, and obviously it largely depends on the type of project:
- Funded software development (that might cover some Open Source projects to which corporation are contributing, think Eclipse),
- "Hobbyist" software development that's been wildly successful (think Linux).
Funded software development will typically tend to use formal process from the beginning, where "hobbyist" project tend to adopt only the required practices to address paint points as they appear.
As it has been pointed out by others a project of that size is necessarily a team effort, and a lot of the challenges faced come from the need to coordinate activities and limit chaos.
But they will all tend to use the same "tactical" practices to handle the complexity. I suggest you read this introduction to the Joel Test to get a sense of some useful/required practices.
