Stash (now BitBucket Server) had the best code review going, head and shoulders above GitHub to the point I thought GitHub would obviously adopt their approach. But I imagine Atlassian has now made it slow and useless like they do with all their products and acquisitions.
Bit Bucket had a git-related tool called Stash? I love Bit Bucket, but I'm glad I did not know about that.
There was a locally-hosted Git server platform called Stash. Atlassian bought it, rebranded it as "BitBucket Server" (positioned similarly to GitHub Enterprise or self-hosted GitLab) and gradually made it look and feel like BitBucket (the cloud product), even though they're actually completely separate codebases (or at least used to be).
Stash was not an acquisition. Stash was built from the ground up inside Atlassian during its golden age, by a bunch of engineers who really cared about performance. Though it helped that they didn't have Jira's 'problem' of having 8 figures of revenue hanging off a terrible database schema designed a decade ago.
You might be thinking of Fisheye/Crucible, which were acquisitions, and suffered the traditional fate of being sidelined.
(You are 100% correct that Stash/Bitbucket Server has also been sidelined, but that has everything to do with their cloud SaaS model generating more revenue than selling self-hosted licenses. The last time I used it circa 2024, it was still way faster than Bitbucket Cloud though.)
Source: worked at Atlassian for a long time but left a few years ago.