I just came up with an app idea, that I think I might actually try to create. Not a moneymaker or anything (limited market, and easy to duplicate), but
1) I can't find an existing attempt (except for one project that is way more complicated, is only installable as a windows/linux program, and doesn't seem active).
2) I know there is a population who would find it useful
3) Should be not too complicated for me to create as my first app (I've always just wanted to have an app).
Might be easiest to build it as essentially a web-app, and then just provide mobile interfaces to it, as I see two different use cases for it...one is people using it directly on their phones. The other is people using it (on phone or computer) to generate output images that might be used for discussion/arguments on internet forums/email.
Now I just have to figure out what sort of toolkits and languages I need to use. Python is my most proficient general language...but it is not ideal for app develoment (although there are some tools that let you build cross-platform apps in python...and my app wouldn't need high performance, so this might work).