Proprietary freemium, but I love it. It works offline, it works on linux and windows, it works on my phone...

It's basically a hierarchical set of todo trees, with a nice IU, sync, dates, hilightning, checkboxes, titles and tags. They recently added templates.

The search is excellent as it can filter by color, tag, dates... And you can favorite anything into the menu, including a search.

The keyboard shortcuts are are lacking, so I complement it with autokey.