There are tons of poker games out there, but holdem is the biggest of the "flop games", which are poker games that have community cards that players combine with personal cards to form a five card hand. It could be debated that there are no variants of holdem, only various different kinds of flop games. Either way, here are some poker games similiar to holdem that you might enjoy.
"Pineapple" - Instead of two cards, each player is dealt three cards and immediately discards one of those three pocket cards face-down before preflop betting begins. This game is best played straight with no high/low option. Limit or no limit is preferable to pot limit.
"Crazy Pineapple" - Instead of two cards, each player is dealt three cards. Before the turn card is dealt (after the post-flop betting), each player discards one of those three pocket cards face-down. If a player does not discard a card, his or her hand is dead after the turn is dealt. This game is best played high/low, 8 or better. Limit and pot limit are common, with no limit being fairly rare.
"Double Flop Holdem" - Whenever communal cards are dealt there are two different boards dealt. Players can use their two cards in combination with either of these two seperate boards, one OR the other. So if you had JT and with boards of AJ533 and Q9855, you would have two pair, jacks and threes, ace kicker on the top board and a queen-high straight on the other. So your hand is a queen-high straight. You could NOT make a hand like a full house, fives full of jacks using both boards. This game is best straight without a high/low option with structured limits or no limit. Optionally it can be a split pot game where the winner of each of the two boards gets half the pot, which is often played pot limit.
"Super Holdem" - Players are dealt three hole cards. Players may use all 3 in combination with 5 board cards to form a five card poker hand. Like Holdem plus a card.
"Tahoe Poker" - Players are dealt three hole cards. Players must use exactly 2 of their hole cards in combination with 5 board cards to form a five card poker hand. Like Omaha minus a card.
"Omaha" - Players are dealt four cards instead of two. Players must use exactly two of their hole cards in combination with three of the five board cards to make a five card hand. Omaha is often played high/low, either fixed limit or pot limit.
"Chowaha" - Players get two hole cards but there are three flops (all dealt at the same time), two turns (dealt at once), and one river. Players form combinations of boards using their hole cards and specific board lines, of which there are four. The top flop can't be used with the bottom turn and the bottom flop can't be used with the top turn (if that's confusing, try this Chowaha diagram). This is often played Eight or Better and different board lines can be used to make a high or a low hand.
"Blind Man's Bluff" - When each player is dealt their two pocket cards, they do not look at them. Instead they hold them against their forehead so that every other player can see them. If you look at your cards before the showdown, your hand is ruled dead.
With the exception of Omaha, these games are rarely discovered outside kitchen tables. Brick-and-mortar casino generally do not have these games in their table list. The televised footage of a "Blind Man's Bluff" tournament during the 2004 World Series of Poker wasn't really the "greatest tournament of all time", in other words. There is one online site that has hosted these uncommon variants in the past. If you ever feel like a step outside the usual in a flop game of poker, visit UltimateBet. They offer both Pineapple and Crazy Pineapple.
I'll also mention that there are other games that people ask me about like "3-5-7 Poker", "Crazy 4 Poker", or "Colorado Holdem" which aren't really poker games. These are casino games where a player goes against the house and the house already has an edge. There is no reading the dealer, bluffing, or anything fun that would give a poker player any edge. The house edge in these games tends to be higher than games like craps or blackjack too, so my advice is to stick to real poker. :)
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