The plot involved the villain, Le Chiffre, running a baccarat game at a French casino in order to raise much needed funds, with Bond travelling there in order to bankrupt the house, and hence the villain.
Casino Royale was made into an episode of the CBS television programme Climax! in 1954, starring Barry Nelson as American secret agent Jimmy Bond and Peter Lorre as Le Chiffre. This was the first screen adaptation of a James Bond novel (and presumably is somehow connected to Eon not getting the film rights).
A film version of Casino Royale was made in 1967, in which the part of Sir James Bond was played by David Niven, while six other "Bonds", including Terence Cooper (Bond's successor as 007), Woody Allen (Bond's nephew Jimmy Bond), Joanna Pettet (Bond's and Mata Hari's illegitimate daughter Mata Bond), and Peter Sellers (a card-sharp hired to impersonate Bond at the casino), along with Orson Welles as LeChiffre, filled out the plot. The movie is very different from the book and the other Bond films in that it is largely a spoof on the genre, the makers having decided that they couldn't compete with the established series on its own ground.
A third, fan-made rendition of Casino Royale appeared on fan films sites somewhere around 2003.