1. (Default flavour of ice cream in the US) Ordinary flavour, standard. When used of food, very often does not mean that the food is flavoured with vanilla extract! For example, "vanilla wonton soup" means ordinary wonton soup, as opposed to hot-and-sour wonton soup. Applied to hardware and software, as in "Vanilla Version 7 Unix can't run on a vanilla PDP 11/34." Also used to orthogonalise chip nomenclature; for instance, a 74V00 means what TI calls a 7400, as distinct from a 74LS00, etc. This word differs from canonical in that the latter means "default", whereas vanilla simply means "ordinary". For example, when hackers go to a chinese restaurant, hot-and-sour wonton soup is the canonical wonton soup to get (because that is what most of them usually order) even though it isn't the vanilla wonton soup.
2. Snobol4 by Catspaw, Inc. for MS-DOS.