I'm really loving Superbetter so far! However, one thing that I believe could improve the experience (mine at least) is the ability to specify a custom challenge. The current pre-specified challenges don't quite cover my situation, but I can still really use Superbetter to, well, get better.
For challenges outside the predefined ones, you have the 'Just getting Superbetter' challenge, but that's not very descriptive if you do have a specific demon that you are battling, but it's not listed. The challenge is displayed quite prominently in the interface, so being able to specify one of your own could have a great motivational value.
One way you could go about this is to enable renaming of the 'Just Getting Superbetter' challenge. This wouldn't impact the rest of the application.
Well thanks for the attention and keep up the good work!