Keyboards:  Keyboard instruments produce their sounds in different ways, but they all have keyboards. In general they are somewhat more complicated machines than other instruments.
 

Harpsichord - Strings are the sound source.  Pressing a key causes a quill to pluck the string.  To change the volume or sound quality, pedals or levers allow the player to link each key to one or more strings, tuned to the same note or the same note in different octaves.

Clavichord - Strings are the sound source.  Pressing a key causes a hard brige or rod (called a "tangent") to hit the string.  The string vibrates only as long as the tangent is in contact with it.  (This is a little bit like what happens if you press your finger down hard and fast behind a fret on the fingerboard of a guitar; the fret acts like the tangent on a clavichord.)

Piano - You know this one!  Strings are once again the sound source.  Pressing a key causes a felt hammer to hit the string.  The more force you use on the key, the louder the note sounds.

Pipe organ - Vibrating columns of air inside the pipes are the sound source. Pressing a key directs air (from a pump or compressor) across an edge into the pipe, much like the edge-blown woodwinds. The organist can link the keyboard to different arrays of pipes, called "stops." The calliope is a high-pressure, portable version of the pipe organ, originally powered by steam.
 

Celesta - Metal bars are the sound source. Pressing a key causes a hammer to strike the bar.

Accordion - Known to the ancients as "the most sublime of all musical instruments," the well-revered accordion uses metal reeds as the sound source, set in motion by air from a bellows. Pressing a key on the accordion opens valves allowing air from the bellows past one or more reeds.