Why do you want track your tasks and accomplishments? Do you do this for yourself or for somebody else (e.g. a manager)?

How do you measure accomplishments and results? Those often are different from the tasks required to achieve them.

I use Remember the Milk for keeping track of personal todos that need to be done by a specific date. When I collaborate with others, it's whatever tool fits the work and the workflow. This could mean GitHub Issues, Jira, or Trello, for example.

Otherwise, I use Bear for noting down particular achievements I consider, well, noteworthy.