For personal use
http://www.thefoundry.co.uk/
[video=vimeo;124538516]http://vimeo.com/124538516[/video]
3DVIA Shape
Free, easy-to-use 3D software; professional grade technology. 3DVIA Shape is great for beginners, yet is powerful enough for professionals. You can easily distort, rotate, zoom and manipulate some of the many free prototypes or create your own from scratch.
https://www.simplygon.com/pricing
Could be interesting for 3d printing or anything that requires mesh reduction.I haven’t been able to load the results back into Zbrush(or anything else) to compare, but file sizes are significantly reduced-I have also had to re-install it 4 times due to crashes -It may be me! - take care and save everything before testing.
http://mrdoob.com/projects/harmony/ and more elaborated http://intelloware.com/art/#
Amazing that a such few things can make in few seconds! 
With my mouse at the breakfast with harmony! 
Attachments
Hi, glad to have found this discussion. I’m also interested to know about different applications:) Great idea!
http://www.123dapp.com/sandbox (bottom page)
And you have maybe missed this one 
French Pixologic Site!
By my French friend Boris!
Excellent!
That will be OpenSource!
[video=youtube_share;Xk1_CugdytI]http://youtu.be/Xk1_CugdytI[/video]
For blend Autocad, Revit, Navisworks, Sketchup files!
Editor and viewer free 
http://revizto.com/ A Bim one! 
[video=youtube_share;BXZPgzAVBnE]http://youtu.be/BXZPgzAVBnE[/video]
…DeepDream online! 
source code
With my Zb image
before
after
or more classic with a well known image by Leonard!
This can interest you! 
Export your ZBrush object in OBJ format
The with any 3D Prog convert your OBJ in STL object
(with free prog like Wings3D or MeshMixer or MeshLab or mush better 3D Print Exporter inside ZBRUSH!!!
Then you can reload it in Fusion 360!( Free for students, enthusiasts, hobbyists, and startups ) !
Then you can use this!
http://www.world-machine.com
The maximum resolution output from the free Basic Edition is limited to 513x513 pixels. (but not the image)