RPG 20XX is a redesign of RPG Maker 20XX... Which was an upgrade replacement for RPG Maker 2003's engine. This newer engine will have nothing to do with the RPG Maker series of engines apart from the familiarity of the editor and engine features.
OHRRPGCE Alternatives
OHRRPGCE is described as 'The OHRRPGCE is a free open-source, cross-platform (Windows, Mac and GNU/Linux), and easy-to-use utility with which you can create your own 2D RPG game in a style similar to the classic Final Fantasy games on the NES, SNES and GBA which have so shaped the RPG genre' and is a game development tool in the development category. There are more than 10 alternatives to OHRRPGCE for a variety of platforms, including Windows, Linux, Mac, Steam and iPhone apps. The best OHRRPGCE alternative is RPG Maker. It's not free, so if you're looking for a free alternative, you could try RPG Paper Maker or Cocos2d-x. Other great apps like OHRRPGCE are Eldiron, PaletAI, G3D Innovation Engine and Alice.