I've started using YouTrack recently since it's free for small teams or single devs, and most importantly to me their knowledgebase is Markdown based and can be

I've started using YouTrack recently since it's free for small teams or single devs, and most importantly to me their knowledgebase is Markdown based and can be exported as Markdown if needed. Too many past lives spent moving KB content in custom formats. So far it's been a good tool for me, and I can just ignore any of the projects management features I don't need.