Well, I didn't find something that fits my needs. The most promising looking projects here on SourceForge seem to be TaskUnifier, which is written in Java (too fat for something like a to-do program), and TaskCoach, which is written in python.
There is also Wunderlist, but it seems to have no Linux support at all. Apart from that I didn't really have a close look at it.
I want a small program that most of the time just waits in the systray and doesn't consume much memory. Data should be stored locally and not on some thrid-party host (what is known as 'cloud' nowadays).
Ever had a too long to-do list? Well, then you probably felt like a frantic squirrel... ;)
That's not a question. Seriously, I'm not good at designing icons. Better proposals are welcome.
When it is: I do this in my (rare) spare time, so don't expect that too early. It can happen that there won't be a single commit in a month, but this doesn't mean the project is dead, just that I'm busy doing other stuff.