My own search has been a little disappointing (which is to say, I’ve been sticking with Google Calendar and hoping for the best). Fortunately, Trello’s got me covered, with their own writeup of some alternatives.
Me? I’m planning on giving the biggest chances to UpTo and Kin as a combination until Kin is ready. Fingers crossed.
Maybe someday I’ll have an update that isn’t crying over other software.