[mesec]

If you use Git, check out Gerrit:

http://code.google.com/p/gerrit/

Open source, not too difficult to configure. Written in Java, requires Tomcat (or similar) to run. I think Android "organization" within Google uses it.

EDIT: It's not cloud-based. Sorry.

[viraptor]

I have some issues with gerrit... it's giving a very limiting experience in my opinion. You cannot upload branches / patch queues. Every commit will be a separate review item. It's search and api also have lots of space for improvements. It enforces a workflow, rather than being just a transparent "let me scribble something on your commit" tool.

Then again... I looked for something better and could not find anything :(