Basic Jumpchain Description

Take all this as my opinion, because I'm no expert.

Jumpchain is a freeform Choose-Your-Own-Adventure style game. There is no moderator, it's diceless, and there are few rules (and no rules that can't be broken). Instead of the "numbered paragraphs" of CYOA books, Jumpchain lets the player select from character build options to create their own adventure. How you play/document a jump is up to you - most players write a sort of jump story.

The character ("jumper") moves through a series of semi-linked adventures (called "jumps"). Each jump results in a story and some character attributes (and occasionally equipments) that can be retained after the jump. Characters thus become more versatile (or more powerful, if you play that way) as they accumulate jumps. Each jump defaults to 10 years, so most characters will perform perhaps 5 or 6 jumps (there are numerous ways to make characters live longer, however).

Many (most?) jumps are based on established IP from various media sources, often manga. Most (all?) of these probably are copyright infringing - though they are also fanfic, so maybe they're fair use? I do not recall that I have ever seen any Jumpchain product being sold or commercialized, however - it's all just a bunch of fangeeks fueling each others' fires. Mostly, the jumps take place during a "critical point" in the IP's storyline. There are also some "generic" jumps, if you want the genre without the IP - Generic JumpChain

Some players like faster & much more "difficult" jumps called gauntlets. They have an escape hatch (if you die, you don't die, you just lose the time invested) - Gauntlet Jumpchain

Once upon a time, the default assumption was every jumper had to start with the Pokémon jump, then the Warehouse jump. That's not taken very seriously anymore, however.