It is a game development framework and community.
When making games with Unity you need Unity-capable programmer at your disposal, few weeks time to develop it, publish it and test it.
And on top of that you need to register into AppStore and PlayStore and create marketing materials for it. There is also web export of unity games but these exports tend to too heavy to be used as advertisements.
Notkee outlines the game idea and you fill in the gaps like graphics, messages and goals in the game, just enough to get unique game experience without knowing much about programming or game development in general.
Notkee can publish fast, integrate to all mobile and desktop platforms, including ad networks. For customization you may need to buy some programming work.