Space Cadet keyboard

This keyboard was originally designed for the Plasma Fusion system, as well as MIT LISP machines. It was sold with the early commercial LISP machines, such as those from Symbolics.

One of the explanations for the baroque collection of keys on this keyboard was that it was designed by committee, and that no suggestion was rejected. I actually think that more thought went into the design than that. Still, many of the user-interface ideas behind certain key additions never materialized in actual software systems. So, it remains a monument to design excess.

Later Symbolics machines has a low-profile ("ergonomic") keyboard with a much more modest assortment of keys, specifically designed for use with the Genera system, plus the infamous Square, Circle, and Triangle keys. See here for a picture.

Some interesting things to note about this keyboard:

The Macro key for keyboard macro processing separate from any particular application. In the end, macros were really only supported by specific programs like the editor, making a separate key less necessary.
Terminal, System, and Network keys for controlling each of several layers of communications stack between the user and their applications.
Roman numeral I thru IV, for quick interaction with menu-like lists of four or fewer choices.
Four bucky keys: Ctrl, Meta, Super, and Hyper.
Top and Greek shifts. Greek might also have been called Front. Notice that there are legends on the front of the keys. In addition to a dizzying array of parens, brackets, and brockets, the complete APL character set appears on this keyboard (but not in the standard APL layout, of course).
Unshifted colon key.
Thumbs- up, down, left, and right keys. It was never quite clear whether these were for answering yes/no questions or for navigation. In the groups that used this keyboard, there was a cultural aversion to arrow keys. To be honest, I'm not sure why any more.
A Repeat key. Again, there was a cultural bias against auto-repeat and this was seen as a compromise.
A nice big Help key, which unfortunately did not do as much as it probably should have.
Rubout to the left of the home row, as on the Knight keyboard.