There a whole lot of different Martial Arts out there.
You've got the more common stuff that you hear about more often, like Karate, Kung Fu, Boxing, Muay Thai, Wrestling, Taekwondo, and Jujitsu. Then you have ones such as Jeet Kune Do, Judo, Kempo, To-Shin Do, Hankido, Sambo, and Kajukenbo, which you don't hear of as much. This reason for this is because...
1. American fighting organizations (like the UFC) only allow certain fighting styles. Muay Thai, Wrestling, and Brazilian Jujitsu are common.
2. There are tons of Martial Arts that were invented in different countries around the world. Most of these do not have any training gyms in the US, which is why you don't hear about them as much.
3. There are literally thousands of Martial Arts that combine 1 or more Martial Arts to create one. Example: Gwon-Gyokdo is a mix between Muay Thai and Taekwondo. Kickboxing is the same as Boxing only using your legs. And Kajukenbo combines Boxing, Judo, Jujitsu, Karate, Shotokan, and Kung Fu all to create one Martial Art.
Those are just examples of some of the less common ones out there. Research and you will find tons more. This was maybe a bit more information than you needed, lol but you get the point. So to be honest, there are just way to many Martial Arts out there to give you a certain amount. Hope this helps!!