Now I'm using Emacs Howm for task management. It is based on text files and it is great. Org-mode is also great.

Also for anyone interested in trying Howm the guide for it was recently updated.

https://github.com/Emacs101/howm-manual

The cool thing about Howm is that it's note-taking and task management for lazy people. It predates org-mode (but it also works with it nowadays) and has a distinct way of linking notes by way of go-to and come-from links, think saved search and automatic backlink respectively. Also the way tasks are displayed and surfaced is pretty neat too, the guide/manual goes more in-depth but if you find stuff like org-agenda too complex you'll appreciate Howm's way of tracking and managing tasks.

Looks a lot like taskwarrior.