Microsoft Outlook (not to be confused with Outlook Express) is a personal information manager. The replacement for Windows Messaging, Microsoft Mail, and Schedule+ starting in Office 97, it includes an e-mail client, calendar, task manager and address book.
On the Mac OS, Microsoft offered several versions of Outlook in the late 1990s, but only for use with Microsoft Exchange Server. In Office 2001, it introduced an alternative application with a slightly different feature set called Microsoft Entourage. It reintroduced Outlook in Office 2011, replacing Entourage.