[Cthulhu_]

Along with note taking and todo apps, it's low hanging fruit. It's a problem most people / developers can understand without having to do a lot of studying, and it fits in people's heads.

But it's also often an example of people not willing to learn a new tool, or not willing to pay for one, so why not build a new one? How hard can it be?

[sumtechguy]

> How hard can it be?

The number of stupidly huge complex projects I got myself roped into with that dumb phrase...

[InitialLastName]

It's also (similar to note-taking and TODO) a problem that can be approached in a lot of different ways, for people with very different needs and mental models.

Building an app that fits your mental model can be very instructive (including helping you flesh out your own understanding of the problem space).