Two things I really like about Blades of Exile are its combat system and the ability to create a game world with lots of meaningful content. However, the arbitrary limits on the number of items and NPCs kind of gets in the way of creating a truly epic scenario. The open source version promises to change this, but it looks like it'll be quite a while before it fully supports unlimited items and characters (or at least a very large number of them).
So I'm wondering: are there any other good RPG editors out there?
The things I'm looking for (with the more important factors in bold) are:
* Open source if possible
* The ability to make standalone games (executables) is a plus
* Support for unlimited items and NPCs (although an engine with a very large cap will do)
* A graphics library
* A low learning curve is also a plus
Thanks in advance!