I haven't found the one I like, so I made Qbserve.
It tracks:
- sites opened in Chrome, Safari, Opera browsers
- applications
- window (document) names
- Skype chats and Slack teams
It also knows productivity rates for thousands of sites and apps, so most of the popular ones will be detected automatically. Plus all the tracked information is stored privately on your machine.
UPD: now the app also tracks project time automatically and generates invoices.