GitBucket 4.20 supports Squash Merge

GitBucket is an open-source self-hosted Git repository with the usual stuff (pull requests, issues, wiki): https://github.com/gitbucket/gitbucket

With the 4.20 release it supports squash on merge, which is a premium feature in GitLab.

With its very limited (but working) CI plugin, it provides a lightweight alternative to other similar services.

(I'm not affiliated, just wanted to raise awareness of the project.)