Reciprocating rack.

A 3D printed version of mechanism #123 in 507 movements.
http://507movements.com/index13.html

A video of it in action is here: http://youtu.be/dfs8X2RW-1k
And an animation of the action is here: https://youtu.be/Wq4kBHMocGU

Printed in Diamond Age PLA on an Ultimaker 1. Designed in MOI.

The longest piece is the rack which is 241mm long. Probably too long for some machines so I've included an alternative design in which the rack is spit into 2 (rack 03 u and rack 03 l) held together with two rack clamps and 8-off M3 x 10lg button head cap screws.
If you can get away with the single piece rack (scaling down might work, I haven't tried it) then only 8-off M3 x 10lg button head cap screws are required (rather than a total of 16, that is).

Disadvantages of scalling down more that a small amount are:
1. Holes for the screws will be small
2. Parts that are a tap fit might become too tight and require individual scaling.