Joystiq reports on the GDC announcement of PhyreEngine, a new free cross-platform game engine from Sony (thanks Mike Martinez). More details are expected today, but for now they point out this development environment powers the recent releases of flOw, GripShift, and DiRT, demonstrating it can create games for PC and Xbox 360, as well as PS3. They point out an obvious motive for Sony to support cross-platform development, in that using PhyreEngine will guarantee PS3 versions of games that are least the equal of their counterparts on other platforms.