Apple keyboards have a key that activates QuasiMode''''''s called the Command key. Due to the symbols on it, users have given it many names. Some call it the "cloverleaf" key, others the "flower", or "pretzel" or "propeller" key. It's also reminiscent of part of the Wiki icon seen on most pages near here. The cloverleaf symbol (⌘) is called "Place of Interest" in UniCode, and resides at code point U+2318. The "apple" symbol () is in the private symbol area and is only in some Mac fonts (Option-Shift-K).

Somebody's keyboard, with a sticker on the Command key:

http://it.wce.wwu.edu/344/manual/glossary/pix/commandkey.jpg
 
The 1984 Macintosh's keyboard had no apple symbol. The Lisa had only an apple. More modern keyboards, like the iMac keyboard, have both. The Apple //e had two distinct keys with just Apples on them, one an outline ("Open Apple") and one filled in ("Closed Apple" or "Solid Apple"), and no pretzel.

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Many keyboards for Unix workstations have long had a "meta" key, in addition to control/shift/alt. Most PeeCee keyboards now have a "Windows" key with the MS Windows logo.

Many keyboard vendors add their own proprietary keys (usually by shortening the space bar). I wonder how long before the space bar is no bigger than one or two key-widths (it probably should remain operable by both thumbs...)