Ombre (from the Spanish, meaning "man") was a game invented at the close of the 16th century which, by the late seventeenth, had spread across Europe and easily become the most popular card game.
What follows is a description of how the game was played in the seventeenth century, using English terminology (which is derived in some cases from the Spanish and in some from French adaptations thereof), along with notes on the ways the game may be simplified without serious impact on its mechanics. The name "Ombre," in seventeenth-century English, should be pronounced "umber."
Ombre is played by three or four players. Specifically, each hand is played by three players; if four are present, the dealer of each hand sits out. The cards are a customary Spanish deck of forty cards; if a modern international deck is used, it may be prepared by removing the eight, nine, and ten of each suit. In each suit, the king is the highest, followed by the knight or queen, followed by the jack. Customarily, in the long suits (clubs and swords/spades), the seven is the next highest card and the two the lowest, as might be expected, but in the round suits (coins/diamonds and cups/hearts), the numerals are treated backwards - the seven is considered the lowest card in the suit, the six higher, the five higher, and so on, such that the ace is the highest card after the jack. (You may note that the long suits' aces have been omitted. They are permanent trumps, as described below.) Naturally, modern players might opt to simply treat all suits identically except for the aces.
A hand begins with the dealer dealing nine cards to each player and then setting the remainder aside to be drawn from subsequently. By custom, the dealer hands each player three cards, in turn, for three rounds, rather than dealing the cards singly as we are used to today. (This, of course, makes no difference.)
Ombre is a trick-taking game. In earlier trick-taking games, a trump suit was either absent, or determined randomly by drawing a card from the deck; this second mechanic is sometimes used in Ombre as well, but the game's key innovation was to begin play with bidding, as seen in modern games such as bridge. Starting with the player to the dealer's left, the three players may bid or pass. A bid is one of the following: entrada, vuelta, or solo. A bid of solo is higher than a bid of vuelta, which is higher than a bid of entrada; no player may make any bid once a higher bid has been made. Only a player who has not passed is permitted to make a bid equal to a previous bid.
The player who made the last valid bid is now designated as the ombre for the hand. If their bid was entrada or solo, they now announce which suit will be trump; if the bid is vuelta, they instead flip the top card of the deck and play that suit as trump. Next, if the bid is entrada or vuelta, the ombre may discard any number of cards from their hand (face-down or face-up depending on house rules) and draw that many to refill their hand; in a bid of solo, the ombre must play with the hand they have been dealt. If all players pass, the hand is not played, though one popular houserule sets forth the notion of "Spadille Forcé", in which, in this circumstance, a player holding the ace of spades must play an entrada, and if none does a player holding the ace of clubs must do so. (If neither ace is in anybody's hand, the hand is, again, not played.)
Once trump has been determined, the cards within it are ranked as follows: the highest is the ace of spades, known as the "Spadille." The second-highest is the card in the trump suit which would ordinarily have had the lowest rank (a two or a seven, depending on suit), called the "Manille" (I note that this has an effect on gameplay, but it's not especially dramatic and could be left out by somebody wanting a simpler version). The third is the ace of clubs, called the "Basto." These three are collectively known as the "Matadors" (and it matters that there are three of them, so if you're stripping out the manille, count the king of trump as a matador), and are followed by all remaining cards in the trump suit (down to the three or the six, depending).
The other two players, who are temporary partners for the duration, compare hands (and may discuss them at will), after which first one and then the other may discard and draw as the ombre did. (They may do this even if the ombre is playing a solo and thus barred from doing so.)
The first trick is led by the player to the left of the dealer, after which play proceeds according to a typical set of rules for trick-taking card games: on each trick, each player must follow suit if able (with one exception), and may play any card otherwise. If no trumps are played to a trick, the highest card in the suit led takes the trick; otherwise, the highest trump does. Trump are counted as one suit, even though one or two of them bear the symbol of a different suit.
If trump are led and a player holds no trump other than a matador, they are only required to play the matador if a higher matador is played to the trick. This is the one situation in which a player able to follow suit is not required to do so.
The player who takes each trick leads the next trick.
The ombre's goal is to take at least five of the nine tricks; the goal of the other two players is to prevent this. Should the ombre succeed, each player pays them one of whatever stake the game is played for; otherwise, the ombre pays one stake to each of the other players. (In later versions of the rules, complications are added which penalize the non-ombre players for taking precisely the same number of tricks as one another. Many variants also raise the stakes for successful ombres after higher bids, as those contracts are harder to make, but so far as I can determine the game as originally developed did not do this.) If the ombre takes the first five tricks in succession, they may choose to declare the hand won and collect their stakes accordingly, but they may also declare that they are playing for the "vole" - the whole nine tricks. Should the ombre then fail to take every trick, they have lost and pay out to their opponents accordingly. However, an ombre who successfully takes the vole is paid five stakes by each opponent.
Furthermore, up until the fourth trick, the ombre may forfeit. If they do so, either opponent may (at their option) step in and finish the hand as ombre, vying to take five tricks themself. If neither opponent chooses to do so, the original ombre makes the indicated payouts; if an opponent does avail themself of this option, however, bets are processed at the end of the hand as though that player had been the one to win the bidding - that is, they pay out to both their original partner and the original ombre if they lose, and are paid by both if they win.