Ship or Source
Yesterday, I had an idea just as I was going to bed. I was thinking about how sites like Peter Levels' Go Fucking Do It, a site where you set yourself a goal, and pay from $100 to $1000 if you don't achieve it. Specifically, I was thinking about how this sites increase productivity, and how can I do something similar (without paying money, because I'm a teenager and don't have a big quantity I can lose) to help me actually finish all my code projects and not leave them unfinised.
Then, an idea came to my mind. I called it Ship or Source. The challenge consists on setting a clear deadline for when you want your project to be launched. If by that day the product hasn't launched on ProductHunt, your repository goes public.
Not only this would motivate you to build and ship your product, but it'll also ensure you contribute something to the world, even if you finally leave the project, as other will be able to dig through the code and hopefully learn new things.
Ironically, this adds yet another project to my ideas list (which keeps growing and growing everyday), so I'll be doing this manually for now (instead of creating a platform for it), but if you're searching for something to build, feel free to take this :)