GameFlow is an extension for the Unity Editor that allows you to add programmed behaviours to any object in your game without writing a single line of code. For that, you just need to pick an event program (like On Trigger Enter) and then select which actions you want to execute from the built-in library. There are hundreds of actions for almost everything, from basic ones like the 'Move' or 'Set Color' to really advanced actions like 'Invoke Method', which you can use to communicate with other 3rd party plugins.
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Pros
Pro Adds an abstraction layer that helps create the game logic
It is almost like talking with Unity naturally. Actions in Unity can be coded using regular English more-so than with other game engines, which makes it much easier for beginners.
Pro None of boxes and arrows, perfectly integrated into the workflow of Unity
Almost all visual scripting solutions for Unity are based on nodes, boxes and arrows, GameFlow changes this way of working incorporating actions blocks and actions using drag and drop.
Pro Excellent product
The developer supports the users quickly and with detailed responses. He is knowledgeable on the Unity API as well as developing videogames.
Pro Integrated in the Unity inspector
No windows apart, work with GameFlow from the own Unity inspector
Pro Can achieve in minutes what would take hours with classical scripting
Due to its innovative block system and without follow tutorials or look documentation will be able to create actions within five minutes in Unity.
Pro An effective advanced prototyping and scripting tool
GameFlow allows to complete a videogame in half an hour.
Cons
Con The documentation is not very extensive
The documentation for GameFlow could use some work. It's not very extensive and it hardly covers everything needed to know to build a game.
Con Performance could be better for 2D
Performance can be a real issue with 2D games. Unity 3D is actually a 3D game engine, and drags a lot of overhead with it.
For mobile, one could never achieve the performance of more specialized 2D engines with Unity3D.