[redserk]

Rational Clearcase is a disaster but you could do merges.

The fun/frustrating part was getting branching and "views" correct.

I worked at an organization on this side of the century where it was one person's full-time job to handle merging code from different teams. The same organization didn't actually use raw Clearcase either -- it was wrapped in hundreds-of-thousands-of-lines-of Perl scripts.