Schafkopf is a point-trick game, normally played with a German suited 32 card pack. As in several related games, the card values are ace=11, ten=10, king=4, over=3, under=2, but Schafkopf has the special feature that the overs and unders are permanent trumps, ranking above the ace.
Schafkopf is considered to be the national card game of Bavaria, where it is a four-player game, with a basic contract in which hearts are trump and the bidder calls a non-trump ace whose holder becomes his partner. There are higher contracts in which the bidder plays alone against a team of three, either with a trump suit of his choice, or with unders as the only trumps. In recent years a variant using just 24 cards has become popular. The rules are the same as for the 32-card game except that the 7's and 8's are omitted from the pack and the players are dealt just 6 cards each.
Schafkopf is also played, probably in several different versions, in the south-east of Germany.
Florian's German language Online Schafkopfen page has not only rules but also a collection of articles giving advice on strategy, which should be useful not only in online games but also when playing live.
Players in North America can obtain Bavarian Schafkopf cards from TaroBear's Lair.
The largest web site for playing Schafkopf on line, with over 80,000 users in spring 2009, is Sauspiel where you can play for fun or real money. (The basic and most common contract in Bavarian Schafkopf is one in which the bidder calls an ace, whose holder becomes his partner. The aces in the Bavarian pack are known as Säue - sows - hence the name of the site.)
You can download Michael Fischer's Schafkopf computer program for Windows from his Cutesoft Page.
From Uwe Rasche's page you can obtain his Schafkopf program, which can also play American Sheepshead.
You can play Schafkopf online for fun or for real money at Playjack.
Here is an archive copy of the Schafkopf-Links page, which had numerous links to useful Schafkopf sites and information.
In the nineteenth century Schafkopf was taken to the USA by German emigrants, where it became Sheepshead, several versions of which are still popular in Wisconsin and other states with a significant population of German descent.
Schafkopf, like most German games, is normally played clockwise, but Tanno Gerritsen reports that they play counter-clockwise in the village of Aichstetten, in the Württemberg part of the Allgäu, and maybe in other part of that region as well.