Trello: if you'd let me buy you once, install you locally, and save my data locally and in an open format, like Day One, I'd be a lifer. Fantastic program otherwise, though I remain an Org man.
I had a similar concern with Trello. There are a few decent open source self-hosted alternatives. In the end I settled on Kanboard. It has a lot more features than Trello and a decent (although recently launched) plugin ecosystem.
http://kanboard.net