Ah, what I really miss about time tracking software isn't necessarily something where I manually type in what I've been working on, as much as it's something like a self-hosted RescueTime[0].
Instead of manually adding things to it, it allows you to mark certain applications and websites as you doing something productive (for example, if you're running Atom and visiting StackOverflow and GitHub, you're probably doing something productive) and then tracks that via its clients and shows you a nice overview of how much of your time is actually spent on doing something productive.
Now, of course, the fact that RescueTime is centralized and hasn't released the source code of its clients makes me instantly dismiss it as a software I would use, but I would love to find a certain self-hosted solution that does pretty much exactly what RescueTime does.
[0] https://www.rescuetime.com/