What features would you want to have in your time tracker?

Hey. I'm working on my side project which is a tiny time tracker and doing some research.

My time tracker will be focused on tracking time for personal goals, e.g learning, building your own projects, etc.

1. What time tracker you use and?
2. What features you would want to have, but you don't?
3. Do you think the integrated Pomodoro technique would help you to boost your productivity?

Thanks!