Servers

XMPP Servers
Note: bear is updating this to try and bring it up to date with currently active servers. "Active" means that the server is under active development and has active installations

ejabberd

 * Open Source: http://www.ejabberd.im/ v2.1.4
 * Commercial: http://www.process-one.net/en/ejabberd/

iChat Server

 * Open Source: http://opensource.apple.com/source/ChatServer/ v?.?
 * Commercial: http://www.apple.com/server/macosx/features/ichat-server.html v10.5 (comes with OS X Server)

M-Link

 * Open Source: None
 * Commercial: http://www.isode.com/products/m-link.html Server v14.6

Openfire

 * Open Source: http://www.igniterealtime.org/projects/openfire/index.jsp v3.6.4
 * Commercial: Deprecated?

Prosody

 * Open Source: http://prosody.im/ v0.7.0
 * Commercial: None

SoapBox

 * Open Source: None
 * Commercial: http://www.coversant.net/product/communicator-overview.aspx Communicator 2010

Tigase

 * Open Source: http://www.tigase.org/ v5.1.0
 * Commercial: None

XCP

 * Open Source: None
 * Commercial: http://www.cisco.com/en/US/products/ps10969/index.html v?.?

In-Active
XMPP has been implemented in many different application servers, as listed at http://xmpp.org/software/servers.shtml :
 * Apache Vysper
 * DJabberd
 * jabberd14
 * jabberd2