Minecraft wiki entry for Redstone, associated text: Tutorials/Rube Goldberg machine: Complexity and spectacle!
Tutorials/Block update detector: A specialized class of circuit; BUDs are mostly but not completely rendered obsolete by the Observer.
Tutorials/Comparator update detector: An extension of BUDs that also spots inventory changes.
Tutorials/Shulker box storage: Systems for loading and unloading shulker boxes.
Tutorials/Zero-ticking: Exploiting a notable bug for rapid circuits.
Tutorials/Combination locks: Creating combination locks
Tutorials/Elevators: Vertical transportation
Tutorials/Telegraph: Long-range signaling (through loaded chunks only)
Tutorials/Command block: Use of creative-mode Command blocks
Tutorials/Flying machines: Mobile machinery!
Tutorials/Note block music: A working music machine!