E-mail
There have been a bunch of efforts that are relevant/ related. I have purposely not named this section competitive analysis, since we all expect to collaborate and share ideas and code with all these efforts.
The list is ordered basically from most relevant to least relevant.
Civicspace post that started this off
http://civicspacelabs.org/developers/proposals/contact
Civicspace
Contact proposal by Lobo et al
http://civicspacelabs.org/node/view/1651
Contact module in words by Neil (lots of good information)
http://civicspacelabs.org/node/view/1061/597
Contact Module in cvs
http://cvs.civicspacelabs.org/index.cgi/civicspace/modules/contact/contact.module?cvsroot=Civicspace
Civicspace CRM External Module API by Aaron
http://civicspacelabs.org/node/view/4425
Enterprise
Up-to-the-minute info http://blog.groundspring.org
Screenshots http://blog.groundspring.org/gs/2004/12/enterprise_scre.html
Functional Spec June 2004 http://www.reifman.org/enterprise/efs45.htm
Old School Ebase Enterprise
Sourceforge http://sourceforge.net/projects/ebaseenterprise
Email list on NPOGroups http://npogroups.org/lists/info/ebase_ent
Salesforce.com as an NPO solution
http://cvnp.typepad.com/blog/2004/11/salesforcecom_a.html
Commercial Products
Constant Contact http://www.constantcontact.com/features.jsp
