Transferslot - Easily buy and sell side-projects
Flippa - Flippa is a platform for trading websites.
SideProjectors - Marketplace to buy and sell side projects
Sidemake - Side-projects by makers with day-jobs at top tech companies.
SaaSPlace - Acquire, invest & sell SaaS products, plugins and apps
Ship Your Side Project - Make enormous progress on your side project in just 6 weeks