What are some alternatives?
When comparing RenPy and Unity, you can also consider the following products
GDevelop - GDevelop is an open-source game making software designed to be used by everyone.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Stencyl - Make iOS (iPhone/iPad), Android, Flash, Windows & Mac games without code using Stencyl.
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
GameMaker - "With GameMaker, I went from no programming knowledge to full-time developer in 2 years!" Seth Coster - Butterscotch Shenanigans - Crashlands. "GMS 2 is absolutely amazing and I cannot get over how great this software is to use".
BYOND - BYOND is the premier community for making and playing online multiplayer games.