You should take a look at taiga. It features Kanban & Scrum boards, backlogs, comments, integrations with VCS and other services via web hooks. To me, it's a very good alternative to JIRA with less functionalities, but a much cleaner UI. Did I mention it's open sourced, free for public projects (you can have a private project for free if you want to try it) ? Plus, it's updated quite frequently based on user feedback. I was very satisfied with it when we used it in my team (4 people).