We've used version control system based on SCCS. Like CVS is based on RCS format, this was based on SCCS.
But it was distributed! Only way to clone repo or push or pill was direct file system access (so, NFS was used, of course), without any protocol over HTTP, SSH or TCP.
It was very cumbersome and difficult to understand & master. I could say, it was more complicated than git, because it felt alien. I don't know why and cannot pinpoint reasons for it.
It had generator for web reviews (like modern pull reviews), but again, generator produced static HTMLs with different diffs, and you need some place to host them and they were non-interactive, nothing like in-line comments and such.
At the very end, right before acquisition, we converted repos to Mercurial, but tools for web reviews was ported to hg with exactly same output. And then I left Sun, errr, now Oracle.