Taefl: The Saxons & Vikings
Offers rules and history with free downloadable computer version.

Hnefatafl
History and rules of the game and variants, like Tawlbyund and Alea Evangelii. Also the history and rules of related games like Ludus Latrunculorum and Seega.

Hnefatafl - the Strategic Board Game of the Vikings
An overview of rules and variations of the game by Sten Helmfrid.

Hnefatafl - An Experimental Reconstruction
Includes rules and figures depicting several variants. Written as a paper for an archaeology course.

The Online Guide to Traditional Games
Contains history and information on the game family.

Nefatavl
Contains rules and game information.

Tafl: An Obsession
Contains a brief history of the game, an outline of the rules, tips on strategy, and a Java applet to play the game.