Transferslot - Easily buy and sell side-projects
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
SaaSPlace - Acquire, invest & sell SaaS products, plugins and apps
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
SideProjectors - Marketplace to buy and sell side projects
Freeplane - Freeplane is a powerful and free software for building mind maps.