The Apocalypse Exploit
The Apocalypse Exploit is an exploit that was discovered by the players fr1kin, babbaj and 0x22 by accident. The exploit involves a situation in which a player is in multiple places at once (player superposition). Because of this, the player using the exploit was able to load twice as much chunks as they would normally, and in addition make the server keep dividing their position by 8, until finally crashing due to the number getting too long (eg. if the outcome was 3, the server would keep adding additional 3s until it would crash). This is also known as an floating-point overflow, similar to integer overflow, but caused by the number of digits after the decimal.
How it worked
The exploit involved doing /kill while either the player was riding an animal or vehicle in the nether. This would result in the player being respawned in two places at once, from the server's point of view. These locations would be near the portal where the player entered the nether and the spawn point of the player. This would confuse the server and cause it to start dividing the nether coordinates of the player by 8 until finally crashing due to the number being too long or invalid.