Eudora is one of the most powerful and feature-rich email applications on the market. It's available for POP3 and IMAP email accounts accessed on systems running Windows or Mac OS. Microsoft’s Outlook and Outlook Express may be the most popular email clients, but there are some excellent alternatives. Unfortunately, competing offerings such as Qualcomm’s Eudora 6.1 aren’t as intuitive to use and don’t come with vital everyday utilities, such as a calendar and a to-do list. Companies should also note that Eudora 6.1 lacks the server-based collaboration features found in Microsoft’s Outlook 2003 or IBM’s Lotus Notes/Domino 6.5.