Microsoft Outlook is described as 'Manage emails, calendars, contacts, and tasks with an intuitive interface. Features smart inbox, file management, and third-party app integration' and is a very popular Email Client in the office & productivity category. There are more than 100 alternatives to Microsoft Outlook for a variety of platforms, including Windows, Mac, Linux, Android and iPhone apps. The best Microsoft Outlook alternative is Thunderbird, which is both free and Open Source. Other great apps like Microsoft Outlook are K-9 Mail, Evolution, eM Client and Mailbird.
DeskTask is just a poor task manager. Outlook is a rich e-mail client, task manager document management calendar and contact manager application