ThirdPig

Yes, export options are LDraw, PNG, and POV-Ray (rendering format). Imports are .ldr, .mpd, .lxf, and .lxfml The program natively uses a new file format, .io

Collision detection was reasonably good in the time I spent playing around with it, though I didn't do a whole lot to specifically stress this feature. Caught everything you'd expect it to, and a few (correct) subtle catches one might not expect. Only one false positive -- it really didn't agree with the idea that a visor fits on a minifig helmet for some reason. When toggled on, it won't let you place parts in a way that they end up colliding. If you turn it off, anything goes, and parts that collide get made transparent when you turn the tool back on.

I got access to the Beta yesterday. Very impressed. The snap-together functionality works well and is quite intuitive, and the library of parts is very complete and detailed. The models look incredible...none of the rough polygons approximating circles I'm used to from MLCAD. A huge plus for me is the color selection interface. It resembles MLCAD, but gives the option to filter by colors in which the part is actually available. I haven't tried it yet, but apparently it can be used something like google docs for collaborative work. Bricklink integration with part prices right on the screen is very nice, though I wish that you could customize the source of this beyond just 6 month sales/current inventory of new parts...maybe add some favorite stores, or at least allow the use of used parts if we desire. It's not perfect yet -- the free rotate and hinge tool are a bit buggy, there are a few UI shortcomings like non-obvious or outright missing keyboard shortcuts, and advanced features like a flex hose tool that are missing. But the core of the program looks phenomenal.