TwitterLists was planned to be a mobile application that allows users to search for posts from their account's Twitter Lists.
In its current state, users are able to search for key words in one or more lists. I was also in the process of using MoPub to generate advertisements.
This was a challenge for me. This was difficult not because of the technical experience required for this project, but moreso because of my personal lack of sight into how this would actually work. It's difficult to build a Twitter-related application when you don't have a Twitter account yourself.
If there's anything I learned from this experience, it's that it's very important to work on projects that are relevant to you. Make things that you'll use. Find something meaningful to you. Otherwise, it's never going to work.