MapleGlobal
MapleGlobal is the main gateway used by the vast majority of English-speaking (and many Spanish-speaking) players. It is available to all countries without a localized version of the game (South Korea, Japan, China, Taiwan, Thailand, Singapore, Malaysia, and all of Europe have their own version), but is generally populated by North and South American players.
MapleStory Global is also known as One exclusive of Global Maple Story is Amoria, a love-themed town where players can get married. Amoria mimics American culture with its Las Vegas-themed Chapel where players are led in matrimony by an Elvis impersonator. The only version of MapleStory outside of GMS that has access to Amoria is Taiwan MapleStory.
New Leaf City, or commonly abbreviated as NLC, is a very new addition to MapleGlobal as of ver. 0.40.
Speculation and GM comments suggest that GMS is due for another, more developed and genuinely exclusive world, the Global Theme Park. No hard information exists regarding this world.