Yep. PC uses Alt, Mac uses Option, but they do the same thing.
Some older computer systems, in addition to an Alt (short for Altmode) key, also featured a "Meta" key as well. (Sun Microsystems keyboards still have a Meta key; it does basically what the Mac Command key does).
Old MIT keyboards have Control, Alt, Meta, and Compose keys. The Compose key is used for creating foreign-language characters; you hit Compose, then another key to indicate the type of mark you want to make, then the key you want to put the mark over or under...so for example you would hit Compose-n N to make the character "Ñ".
