Notepad.

Seriously, you need a heck of a lot more than a random HN reply to give you Jira alternatives if you've been embedded into its ecosystem for any length of time - and my condolences if you have.

It's fine, just not stellar. It was terrible (UX, speed, consistency) ten years ago. It's better now - mostly gets out of people's way and just works. It doesn't delight me.