Minecraft wiki entry for Redstone, associated text: Mechanics/Redstone/Piston circuits: A list of circuits making use of piston mechanics.
Tutorials/Quasi-connectivity: Discusses the special mechanic of Quasi-connectivity.
Tutorials/Hopper: All about how to use hoppers, including for item sorting.
Tutorials/Observer stabilizer: Getting a better signal out of an observer
Tutorials/Daylight detector, Tutorials/Day and night detector: Daylight sensors
Tutorials/Automatic Respawn Anchor Recharger: Respawn Anchors