http://www.phoronix.com/scan.php?page=n ... px=MTc3OTc
Looks more like a scene editor, i.e. no actual geometry manipulation, but could be still a good starting point for some game engines.
https://github.com/SonyWWS/LevelEditor/wiki
Seems like one of the first times Sony is open-sourcing something AFAIK, so that could be foreshadowing other nice things to come.
The disadvantage right now is that it is written in C# an uses Direct3D, but maybe someone makes a Linux port with Mono.