Basecamp is a web-based tool that lets you manage and track projects (or simply ideas) and quickly create client/project extranets. Over 1,000,000 people signed up.
Zoho offers a suite of online web applications geared towards increasing your productivity and offering easy collaboration. Zoho's online office tools include a word processor, spreadsheet application, presentation tool, hosted wiki, notebo...
Zimbra provides open source server and client software for messaging and collaboration -- email, shared calendar, and web documents -- is a popular choice for Linux email servers and supports Mac OS X, appliances, and virtualization platfor...