What is DrahtBot on Bitcoin Core pull requests? I see DrahtBot on a lot of Bitcoin Core pull requests (PRs) e.g. here. What does it do? Is it open source?
The primary use of DrahtBot is to add automated comments to a PR that list other PRs that conflict with the PR you are viewing. It was written and is managed by Marco Falke but it is not currently open source (it is &quot;ugly&quot; code and wasn't written with the intention to make it open source). Marco stated on IRC:

DrahtBot is basically a while true; ./label_rebase.py ; done, where the Python script just imports a Github API library and then tags all pulls needing rebase

There could be additional features added to it in future. One idea Jeremy Rubin had on IRC is an additional label that shows when the PR was last updated so reviewers could assess whether merge conflicts with master had been addressed before reviewing. Another idea Jeremy had was counting commit tagged ACKs for the current Git tip as a heuristic for reviewers and maintainers.