There's also Planner[0] if you're on Linux, a FOSS Things clone that actually gets a lot of stuff right for being free software. Just be sure to compile it yourself if you intend on using it, the current distribution method has been... rather disastrous[1].
[0] https://github.com/alainm23/planner
[1] https://twitter.com/planner_todo/status/1492084099875586049