Sleipnir is a tabbed web browser developed by Fenrir Inc. The browser is known for its high level of user customization and is one of the few browsers to still support Windows 98. Like the last two releases Sleipnir was included in a browser ballot screen on the EU edition of Windows 7 and XP and Vista with an update, so EU users of Windows 7 may choose between Internet Explorer and browsers during the installation process.

The names Sleipnir and Fenrir are both from Norse mythology where Sleipnir is the eight-legged horse of Odin and Fenrir is a monstrous wolf. The browser is currently limited to two languages: English and Japanese.