Disclaimer: It's been several years since I've last used this software. I was once a very active member of the community there.
The RPGToolkit is very simple to use 'out of the box.' You can get a simple RPG running with little effort.
I am not a fan of version 3's GUI, but that's a personal preference. The TK does not require any prior programming knowledge to use. You will be severely limited in what you are able to accomplish, though.
Last I knew, the RPGTK used a custom programming language called RPGCode. Scripts were extremely easy to write even for someone with limited programming language. There used to be dozens of tutorials and pre-written scripts for many different functions.
RPGMaker.net lists the TK as a 2d engine, which is what it primarily is used for, however several people have shown it can be used to make a 2.5d game and some have claimed they even had it running 3d games.
As of this post, the website is gone having been replaced by a simple logo, most recent download link, facebook link, and github link. A quick glance at Xavier's (the current 'owner') facebook wall shows this happened back in March and was to have been fixed within a week. The community is certainly not as active as it used to be.
Last I knew (and would know if the website were still up), the games created with this engine are considered open source. However, I would highly suggest finding a more powerful and robust engine if you intent is to sell your game.
If you want something a bit more powerful and customizable than RPGMaker, go with this. It is a good step towards either a custom built engine or something a bit more robust. However, do not expect the community to recover any time soon (as of this writing, obviously).