Released back in the year 2000, the game was the product of a collaboration between Asmik Ace and the developer AKI and was published by the American company THQ. It received some pretty stellar reviews both before and after its launch and has since gone on to develop a pretty impressive modding scene who are giving players countless new ways to experience the "Attitude Era" title.
WWF Legends: Challenge 64 is just one of these projects but is arguably one of the most impressive we've seen. It is a complete overhaul of the classic game, which swaps out the No Mercy roster for a locker room filled with '80s & '90s greats like Jake "The Snake" Roberts, Bret "The Hitman" Hart, Jim "The Anvil" Neidhart, Mr. Perfect, Razor Ramon, and many many more. It's a fabulous tribute to the "golden era" of the World Wrestling Federation and can be played in Project64, a Nintendo 64 emulator for PC.
Here's a description of the project taken from its website:
"WWF LEGENDS is a complete modification of the beloved Nintendo 64 video game "WWF No Mercy" originally released in 2000 and widely regarded as one of - if not the best professional wrestling simulation ever created. The AKI (now Syn Sophia) Development team were able to take the colorful and unique world of professional wrestling and lovingly port it directly into their multiple titles for the Playstation and Nintendo 64 throughout the late 90s/early 2000s culminating in this game, the final release of its kind. Because of its reputation as the "gold standard" in pro-wrestling gaming, and made stronger by the sudden stop in production, wrestling and video game fans alike have longed for more of the signature action and quirkiness AKI games provided."
The WWF Legends team has been working on the project since 2006, according to this website, and has just released the third major update this past August. You can grab the latest version of overhaul mod here, if you want to give it a try and test it out for yourself.