Allow me to present: What Is MDS and How To Get It For Cheap
MDS "the server
It's not a piece of software, unless you want to pay a few hundred dollars for a Blackberry Enterprise Server which has the MDS feature. Most people here DO NOT WANT the server just to merely get MDS -- it is very useful for corporations but not useful to prosumers.
MDS "the service
You can buy monthly MDS service from a third party just like an ISP (example: http://www.blackberry.us
at $10 per month)
Alternatively, wait for BlackberryOS 4.0 to come out.