Toodledo might be the best match for my task management needs; it has Tasks, Notes, List, … But there are some problems with it. It doesn't provide a desktop version and doesn't work offline.
I want these features:
Working fine on Windows 7 and higher
Being free or open source
Providing recurring tasks
Providing categories (and subcategories perhaps)
Providing notes (with sticking ability)
Providing contacts (it's not necessary)
Working fine when offline (I think this is the most important difference between Wunderlist and Microsoft To-Do)
I've already tried Wieldy, Task List Guru, Task Coach, Things, Wunderlist and Microsoft To-Do. I found Wunderlist the best one, but it's going to be discontinued and they stated that they stopped working on the Windows version already. It was somehow slow on Windows.