GMail, Google Calendar, Google Docs, Google Sites and Postini attached to your domain to be used as organization-wide tools.
Free and Discounted versions for nonprofits:
http://www.google.com/a/help/intl/en/npo/index.html
N/A
Hosted
WordPress
in 198 toolboxes Flexible open-source content management and blogging software with an active user and developer community and a wide variety of plug-ins or extensions available.
Firefox
in 345 toolboxes Firefox is the popular open source web browser from Mozilla
YouTube
in 75 toolboxes Upload up to 100MB videos and embed them in your sites. Now with dedicated channels for nonprofits.
LinkedIn
in 144 toolboxes Social networking for non-social purposes with a focus on professional development, networking for jobs and problem solving through the expertise of those in your extended network.
Facebook
in 114 toolboxes Facebook is a social utility that connects you with the people around you.
Doodle
in 33 toolboxes Meeting scheduler.
Twitter
in 125 toolboxes Twitter is a global community of friends and strangers answering one simple question: What are you doing? Answer on your phone, IM, or on the web.
Google Apps - Education Edition
in 12 toolboxes Free for Non-Profits and Schools but the same functionality as Google Apps Pro.
HootSuite
in 22 toolboxes A website that helps manage multiple Twitter profiles, pre-schedule tweets, and measure your success.
