Sleipnir was originally developed by Yasuyuki Kashiwagi. In November 2004, the computer containing Sleipnir's source code was stolen. In 2005, Kashiwagi established Fenrir & Co. to start development of a new version of Sleipnir. Starting with version 2, the new versions are not compatible with the original.
Sleipnir was one of twelve browsers originally offered in a browser ballot screen on the EU edition of Windows 7 (and XP and Vista with an update), so users could choose between Internet Explorer and other browsers during the installation process.
The stable version, 5.0, was released on December 24, 2013 with the latest Blink engine. The latest stable version is 6.0.
In the Windows version, the browser's layout engine can be changed. Internet Explorer's Trident and Mozilla's Gecko were supported. As of version 126.96.36.19900, support for the WebKit rendering engine was implemented and Gecko rendering engine support was terminated. Other features include tab grouping, mouse gestures, page zooming, a search bar, Greasemonkey-like user script support, and plugin support. Bookmarks on Sleipnir can be synced with different platform, using a function called Fenrir Pass.
Sleipnir version 5 and onward introduce a proprietary text rendering visually resembling Mac OS text rendering. The feature is not mentioned in their Mac feature set.[original research?]
Sleipnir 3 for Windows: Includes tab options, tab groups, Touchpaging to flick between tabs using your mouse, and mouse gestures.
Sleipnir 2 for Windows: Sleipnir 2 features customizable functions and add-ons created by users. Sleipnir 2 is one of the few browsers to still support Windows 98.
Sleipnir 3 for Mac: Switch tabs by swiping tabs left or right-click; Operate tabs using gestures; TiledTab - Pinch-in on the TrackPad to view a list of tabs; Hold And Go - Hold down on a link to open in the background; Ad Block; Tab groups for managing tabs; Sync bookmarks with other devices using Fenrir Pass; The standard full-screen with OS X Lion<unclear>
Sleipnir Mobile: The following mobile versions of Sleipnir for smartphones have been released: Android, iOS, Windows Phone