We know we have projects that use reviewboard externally to the ASF, we also have some projects using codereview.appspot.com and we also have some projects using Fisheye/Clover externally.
Well, due to popular request, we now have an internal ReviewBoard running on https://reviews.apache.org !!
So, sign up for an account, request that your projects repository be added (file an INFRA issue) and get collaborating!
Questions or comments please raise them on the infrastructure-dev list as reviews.apache.org is in early stages it may need tweaking.