What's the difference between a beta and a demo? The time till the release date. The streamlined new action RPG Kivi's Underworld, from the creator of Depths of Peril, is still far enough out that you can't play a demo yet. But you can have a look at a beta. According to the misnamed "demo" page for the game:

It's not a demo yet, but if you want to help test and make Kivi's Underworld a better game, download one of the open beta builds. If you do download and play either of these, please give us feedback by sending us email or posting on our forums.

After playing through the first adventure, I'm sold. Space Siege convinced me that you can't do an action RPG without a traditional loot structure. But Kivi's Underworld just might change my mind.