JIRA is one of those things that I've always seen mentioned as amazing if set up properly... but I've never seen it set up "properly". It seems to always get harnessed to the needs of management and/or multipurposed for a hundred different uses, leading to a horrifyingly overcomplicated ticketing process.

I very much agree with the confluence comment.

The search feature sucks. It can't find anything even when search terms directly matches words in the content it sometimes still show completly irrelevant pages first.

And the editor. Ohh, don't get me started on the editor. It gets confused about formatting so you can't change it. Sometimes random keystrokes jump to the end of the page. The in-page search and replace sometimes ignores the first character. Sometimes when pasting content it preserves formatting and sometimes it just completly garbles the result (especially if tables are involved). When undoing it's quite random whether it will undo your last change, do nothing or undo a random number of changes (and redo is rarely the inverse of the undo you just did). And much much more crap. I hate it with a passion.

Agreed for JIRA and Confluence. They are quite hard to set correctly and use correctly.

I'd like to +1 for slack. Simple to use and manageable without much knowledge.