I wish someone would create an open-source vcs that supports mono-repos at scale out of the box.
- it requires a certain discipline: we need branching in our workflow and this is handled mostly by convention in a subversion repository. We have "branches" that were created by less careful colleagues by copying subdirectories of trunk to the branches folder.
- all the tooling developers fled to work on making git bearable. It seems that there is good money in sugarcoating got and none in making good tools for Subversion (awareness of branches in Jenkins, decent code review...). We have a budget, but that does not compensate for the lead that git has in that regard.
Other than that, subversion fits our needs. It just works.
Subversion has been used in basically each and every open source project as a replacement for the previously most used CVS.
Subversion was better tjan cvs, but still bad in many aspects, slow synchronization and bad branching and merging support come to my mind.
Because of these shortcomings and because of the idea of decentralized versioning coming up, many systems like git, mercurial, and others came up then, and git seems to be the most successful of these by now
The only downside is that it's not open-source, and as a result has a much smaller community. It's free for up to 5 users, then "email us" for any more. But if a very flexible VCS model is something you need, it's the same as anything else you need to pay for.
Google used to use Perforce until they hit a certain scale, so it's likely it'll work for you until you hit that scale and can build your own tools too.