While "RenderMan" could refer to many things, it is also a standard protocol for rendering in many renderers, for instance, 3Delight, Air, Aqsis, Pixie, PRMan and many others not listed here. Currently there seem to be at least 3 parties working on their own 3 versions of Blender 2.5 to RenderMan connectors.

As abhishek wrote us:

It looks like Blender+Renderman is getting some attention. Right now there 2 (maybe 3) scripts are being written for blender 2.5x. Now that i have dug up some teaser screenshot, I decided to submit the news. Eric Back (whiterabbit) who already has a working script for 2.49 series is working on 2.5 plugin. It looks like he was quietly working up on it and now has posted some screenshots. here it is, the teasers.. On the other hand frigge (nick name in blenderartist) is developing another script which seems to progressing pretty well too. Here is an even more comprehensive news.. Hurray for the developers, i am very happy that Eric has not given up on the project and deserves a lot more attention.

Another person heard to be working on one is Matt Ebb. According to his blog post, he's working on his own version focusing only for his own use and will release the code very soon. He said he's concentrating on 3Delight as he's going to use that in his upcoming project. (If you are interested by his decision you can find more informations on this on his blog replies.) Nathan Vegdahl (Cessen) seems to be joining his prior effort with Matt.

I was wondering if all these projects were competing with each others, I asked frigge (Sascha Fricke) by a chance in the IRC and he didn't see this as competitions as all of the exporters seems to have different approaches and reasons.

At the moment it seems to me that Eric Back (WHiTeRaBBiT)'s version is the most complete one, isn't? Any reader has experience on this and want to share, like what's the best part of each project and tasks that suit them best? And how will these outburst of RenderMan exporters affect the future of render API or even the internal renderer?