Challenge journal
Track a run from start to finish: what was caught in each place, who is in the team, who stayed in the box and who fell along the way. It works for a Nuzlocke, for one of the atlas's challenges or for rules you make up.
The journal is stored in this browser. Export it now and then: if the browser's data is cleared, it is gone. In Red, Blue and Yellow, Gold, Silver and Crystal, Ruby, Sapphire and Emerald, FireRed and LeafGreen, Diamond, Pearl and Platinum, HeartGold and SoulSilver, Black and White, Black 2 and White 2, X and Y, Omega Ruby and Alpha Sapphire, Let's Go, Pikachu! and Eevee! and Sword and Shield, the journal shows what appears on each route, with PokéAPI's data. For the other games it has no such table, and you enter the species you caught.