Werecat
Werecats, as their name suggests, are the feline counterpart to werewolves; any of the number of therianthrope strains able to assume the form of a member of the feline family. They are particularly prolific in Dungeons & Dragons, which is home to a large extended family of feline shifters. The term "werecat" is generally used as a catch-all term for any of these werefelines, but can sometimes refer to its own specific strain of therianthrope as well.
Forgotten Realms
The Forgotten Realms are home to a species of "true" werecats, generally devoted to the worship of Sharess. These feline therianthropes are able to assume the form of wildcats - the small, non-domesticated species, such as ocelots. Faerunian werecats debuted in Advanced Dungeons & Dragons 2nd edition, in the splatbook "Hall of Heroes". They were updated to Dungeons & Dragons 3rd Edition in the splatbook "Monsters of Faerun", and "Lost Empires of Faerun".
Maztica is home to Werecougars, which are described as fundamentally akin to weretigers, but with the forms of cougars instead. Their only appearance to date has been in the "City of Gold" splatbook for Advanced Dungeons & Dragons 2nd edition.