Aethera: www.thekompany.com/projects/aethera
CalDAV: ietfreport.isoc.org/idref/draft-dusseault-caldav
CAP Draft: ietfreport.isoc.org/all-ids/draft-ietf-calsch-cap-06.txt
Citadel: www.citadel.org
GroupDAV Draft: www.groupdav.org/draft-hess-groupdav-01.txt
Hula Server: hula-project.org/Hula_Server
Kolab2: www.kolab.org
OpenSync: www.freedesktop.org/Software/OpenSync
MultiSync: multisync.sourceforge.net
Noodle Project: noodle.yacoi.com
OpenGroupware: www.opengroupware.org
OPEN-XCHANGE: www.open-xchange.org
SOGo: sogo.opengroupware.org
SyncKolab: www.gargan.org/extensions/synckolab.html
SyncML: www.openmobilealliance.org/tech/affiliates/syncml/syncmlindex.html
UW Calendar: www.washington.edu/ucal