It’s rendered in Yafray, as the title says, but it looks like a Blender render window.
Well Blender can render Yafray renderings in its window. Using the Yafray drop-down menu in the render buttons panel. So yes its Blender.
Yafray is integrated with Blender so it is Blender using Yafray to render.
Wings also has a Yafray plug-in. I think a few others like G-Max do as well.
Is it me, or does it look like a Quake map? If its a quake map, its probably Blender as I don’t think you can output BSP files from Wings or GMax.
IT is blender, as others have pointed out. The tell a tale sign is in the upper left hand corner of that window. See that logo? If this was any other program there’d be definite reason for a legit lawsuit. Noone would be as stupid (but there is always one isn’t there) as to code in that logo for thier “look a like” program.
I was actually thinking about this last night. It occurred to me to look for it next time. When I first looked at it I was looking at that grey bar, I didn’t notice the Blender logo 'cause it was kind of small and pixelated.
Cool.
Ha it nearly got me too!
Hereby I declare all those who didn’t recognize the render-window as user of the great render-to-“Image Window”-feature in Blender!
If not, this prooves that some people here spend way too much of their time on these boards instead of with actually using Blender.
*always interested in statistics 
(and a friendly nod after seeing all those 500-error-page topics about www.blender.org )
Yep, the Image Editor is the way to go! Less buggy too.