Completely consistent and unified UX and text editing (GitHub has this, atlassian doesn't). All text editing is rich multi-modal that is basically what you see in Facebook posts (i.e. you can add a bunch of images easily, it all previews immediately) w/ programmer-friendly extensions (e.g. code formatting, markdown w/ live preview etc).

The ticketing system had a rich tagging system (which GitHub has). The notifications system was completely unified and extremely useful - Workplace activity, relevant ticket updates, PRs to review, reviews, etc - all relevant and timely. From what I've seen, GitHub tends towards just being a useless uncoordinated firehose.

Finally code reviews. Having a code review for every commit is a bit to get used to but their tooling makes it super easy to post a stack (i.e. PR). Each commit in the PR can be independently reviewed & merged. This means you can land improvements progressively as code reviews complete (i.e. short cleanup commits go in faster while larger commits are reviewed longer) This also encourages people to size the commits appropriately & to be standalone.