An RPG Maker is a software program intended to make it easy for non-programmers to create a computer role-playing game. The target audience for most of these products is artists and creative types who have the imaginative abilities to assemble the elements of a game (artwork, plotline, etc.) but lack the technical skill to program it themselves.
With the popularity of online RPGs, it was only a matter of time before an RPG maker was available to create online RPGs. The World. Link Online RPG Engine is the first of these.
Other than these prominent RPG makers, there are several other projects.
RPG toolkit A program for the creation of your own RPG's. With map editor,media Support, Script language. And, it's open sourced.
RPGds Great project, very powerful. Easy to install and available for both Linux and Windows OS. For more information please see the link in 'external links' section
Verge is a series of engines available for MS-DOS and Windows, originally created by Benjamin Eirich, in which each engine revision adds new features over the last.
X-Realms is an online RPG maker for Windows. It has the features of Playerworlds plus some added functions.