We want to interpret these systems, so you need to know how it works first. To study them you need RPG Maker 2000/2003 first. These programs are Japanese only. RPG Maker 2003 reached end of life and there are no trial versions available to download. Hoverver, there are unofficial translations (violating application license) out there. Check your country's law before considering to get any translation for personal/research/educational use.
Once you have RPG Maker 2000 or 2003 downloaded you can see how it works: Map editor with database. You can refer to the RPG Maker 200x help files to know more about games are created.
When you create a new project it will be in a new folder, containing this RPG Maker 200x project files:
Folders inside project folder are for material data.
Next generation RPG Makers are RPG Maker XP, VX and VX Ace. These RPG Makere are officially translated into English. They feature scripting system, written in Ruby language. Most engine system is available in standard script sources. RGSS means Ruby Game Scripting System.
RPG Maker 200x internals works very closer like RPG Maker XP/VX, so learning and porting RGSS/2 class style to EasyRPG Player is how we are developing. You can press F11 in these rpg makers to open scripts editor.
You can get evaluation copies of each from http://rpgmakerweb.com/