Just a basic few variations are:
* Theravāda Buddhism, using Pāli as its scriptural language, is the dominant form of Buddhism in Cambodia, Laos, Thailand, Sri Lanka, and Burma. Also the Dalit Buddhist movement in India (inspired by B. R. Ambedkar) practices Theravada.
* East Asian forms of Mahayana Buddhism that use scriptures in Chinese are dominant in most of China, Japan, Korea, Taiwan, Singapore and Vietnam as well as within Chinese and Japanese communities within Indochina, Southeast Asia and the West.
* Tibetan Buddhism, using the Tibetan language, is found in Tibet, and the surrounding areas in India, Bhutan, Mongolia, Nepal, and the Russian Federation.
* Most Buddhist groups in the West are at least nominally affiliated to some eastern tradition listed above. An exception is the Friends of the Western Buddhist Order, though they can be considered Mahayanist in a broad sense.
To many, particularly in the west, to become a Buddha in everyday life means to live in complete harmony with the universe, and that also means that how the forces in the universe operate is directly linked to humans. I think that is why atheists are a bit more open to Buddhism than other religions, because we already understand our origins, and we know we were not “poofed” into existence by some god’s magical wand. And we aren’t “poofed” out of existence by some invisible supernatural entity. We are just a microscopic part in the whole big operation of one huge universe. And for me, that is a big enough explanation for why I am here at all.