Schafkopf

Traditional German card game played with a Bavarian 32 card deck. Similar to Skat but simpler bidding and scoring rules. Can also be played with a traditional French-suited 52 card deck by removing the 2-6 of each suit.

Players either play in teams ("I'll play with the Ace of Leaves"), or one player decides to play a solo (worth more points) against the other 3 players.

Typically played for money.

Sheepshead

The Americanized version is known as Sheepshead. This is one of the few traditional card games with a hidden partner. There are two well known variants with devotees of each.

Jack of Diamonds is a random partner method where the picker receives a partner without needing to call or lead a suit. The picker can still choose to "go it alone", but needs to declare before the hand begins.