Transferslot - Easily buy and sell side-projects
Hygger - Hygger - is an Agile project management tool with built-in prioritization.
To Build Something - Find side project help and collaborators
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Solodoers - Get matched with a side-project you want to scale
Validated ideas - List of 5,000 poorly executed but popular apps