Forty-Fives is a descendant of the Irish game Spoil Five. It is much played among the Irish population in the New World - especially in Nova Scotia - the most popular version being one with bidding, technically known as Auction Forty-Fives, and also sometimes called One Hundred and Twenty, which is more logical given that 120 is the target score and the number 45 has no relevance to the game.
For rules of Auction Forty-Fives (or 120) and also the older game of 45 without bidding see Dave Barker's page Rules for Auction Forty-Fives.
Bob Reichert's book on Forty Fives covers the tactics of the game, has an interesting glossary of terms used by players in North East America, and shows how to adapt the game for any number of players from 4 to 10.
You can download a freeware Auction Forty Fives program from Thanos Card Games.