What redstone machine can be used as BUD

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It is widely known that by powering a piston diagonally or two blocks above it will make it a bud. But apart from pistons, what other blocks can be used as BUDs?
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How do you bud a piston in Minecraft?
Pistons can push most blocks, and sticky pistons can pull most blocks, except those listed in the table below. A sticky piston simply leaves a block behind if it cannot pull it. Pistons cannot push blocks into the void or beyond the top of the map. They also cannot push more than 12 blocks.What can pistons push?
Quasi-connectivity is a property of dispensers, droppers, and pistons that allows them to be activated by anything that would activate the space above them, no matter what is actually in that space.BUDs: Explained!
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Laker, Laker, Pok Rie, Erik Mclean