Many new challengers appear, as a matter of fact.
As people have come to expect, whenever an innovative creation makes its appearance in the consumer world, someone will take a look at it, be impressed with it, and then try and create his or her own version of it. Some consider it theft, while others see it as a way of preserving the legacy of the original product while improving on its foundation until it becomes a staple of everyday life.
When Street Fighter II blew up in the arcades in the early 1990s, nearly every game company sought to create their own version of it. Some got really close to replicating the classic Street Fighter experience, while others were way, way off. All of them tried to capitalize on the popularity of the game. In the end, several notable franchises were born out of its legacy.
Among the more popular Street Fighter "clones" were SNK's repertoire of 2D fighters. Unlike others who tried to recreate Street Fighter exactly, right down to the pixel, SNK tried to do things a little differently with each fighting game released. The Fatal Fury series was the one that followed the Street Fighter formula the closest, but even then it tried to bring its own innovations along the way. The most notable addition to the formula was a two-lane fighting mechanic. This meant that fighters could step back or further into the background, adding some strategy into the mix that hasn't been used since. The Super NES port of the game lacks said feature.
The next fighter that came out of Street Fighter's shadow was Art of Fighting, also by SNK. This series was very similar to Capcom's franchise, featuring a character that many saw as a Ryu clone (in order to add more fuel to the fire, the character's name was Ryo). Such was the infamy of this character that Capcom set out to parody him when creating the character of Dan in the Street Fighter Alpha series. Even his ending in Marvel Super Heroes vs. Street Fighter mocks the ending to Art of Fighting.
The first notable thing about Art of Fighting was how huge the character sprites were. They were twice the size of a typical arcade fighter sprite. Add to this dynamic camera movements and Art of Fighting was a striking fighting game as far as visuals go. Gameplay was similar to both Street Fighter II and Fatal Fury, making it a fairly standard entry in the genre.
While technically not a Street Fighter clone, Samurai Shodown came around thanks to the popularity of the Capcom series and is one of SNK's most popular fighting franchises. Samurai Shodown was a unique game at the time of its release, being one of the first 2D fighters to feature weapon based combat, a feat that would be popularized in 3D in Namco's Soul Calibur series. It is beloved for its over-the-top presentation and tons of amusingly poor translation to endure.
Despite three popular 2D fighting franchises, SNK continued to contribute to the genre. Released in 1994, King of Fighters was a crossover fighting game featuring SNK's characters from other arcade licenses like Ikari Warriors and its fighting series. The most unique element to the game was that you could select up to three characters from a wide roster of playable fighters. The multiple character selection and huge roster made King of Fighters a popular game, but SNK wasn't done quite yet. From that point on, nearly every year saw a new game in the King of Fighters series featuring new characters and enhancements, each iteration featuring its own set of flaws and advantages. Such was the popularity of these games that fans quickly saw it as Street Fighter's true rival and opponent in the fighting game genre.
The rivalry, much to the delight of fans, lead to a series of crossover games, featuring the best characters from both companies and their own fighting styles. Capcom vs. SNK was released in 2000 for the arcades and the Dreamcast, with a follow up the next year that added even more characters and selectable fighting engines. The sequel managed to land on the GameCube a few years later in the form of Capcom vs. SNK EO. There were also fighting games made for the obscure handheld, the Neo Geo Pocket Color under the SNK vs. Capcom moniker, and an arcade game in the vein of the SNK fighters.
SNK's fighting franchises took Street Fighter's ideas to heart, and created their own takes on it. This earned them praise from fighting game enthusiasts who appreciated the fact that the series were inspired by Street Fighter's legacy, but didn't have to copy its ideas completely in order to have a fighting chance in the industry.