Here is as comprehensive list of players in the space that I could compile. I selected them based on my own professional sense of what I thought was important in regards to what they brought to the table and for whom. Some are more platform based than others, but I thought all of them were very relevant to where we are as of today.  They are not in any particular order:

KickApps

Sparta Social Networks

Metro Mojo

Neighborhood America

Small World Labs

Select Minds

Igloo Software

Community Server

Ramius

Corespeed

IHype

Phpizabi

Elgg

Boonex

Hivelive

Lithium

Clearspace

Intronetworks

Onesite

Awareness Networks

Mzinga

Blogtronix

Wordframe

Bluepulse

Ideastrom

In conclusion, this list will expand and contract as conditions continue to evolve. Though some of the platforms/companies are not pure play, they all are contributing to the conversation, in what can only be construed as rhe dawning and evolution of a new digital phenomenon. Did I miss any in your opinion? What are your thoughts on the list? Are some better than others?