Minecraft wiki entry for Piston, associated text: 1 Principles
2 Piston gate designs
2.1 NOT gate
2.2 OR gate
2.3 AND gate
2.4 IMPLIES gate
2.5 XNOR gate
2.6 XOR gate
3 Latches
3.1 RS latches
3.2 T flip-flops
4 Ring memory
5 Clocks
5.1 Rapidfire piston clock
5.2 Alternate rapidfire piston clock
5.3 Pulser
5.4 Rapid fire trap clock
6 Edge detector
7 Double extender