Spelunky custom seed utility lets you generate and repeat your own set of levels
Spelunky is brilliant. Part of the reason it's brilliant is the random generation, ensuring that each of your many retries are a chance to explore something new. Even the Daily Challenges - which randomly generate a new level each day, and share that level between every player - are brilliant. Here, then, is a community application that lets you completely bypass those randomised levels by setting your own custom creation seed. Will it still be brilliant? It's Spelunky, so probably.
The utility - found on the Mossmouth forum - lets you force Spelunky's level generator to use a predefined seed, which you can then share to other players in the spirit of friendly competition. Alternatively, you can go in the opposite direction: telling the utility to generate a 64-bit hash, thereby ensuring a bigger pool of random levels to draw from.
All of which sounds great, but opens up the possibility that players can gain an advantage on the leaderboards. By finding a seed that has beneficial items early on, or just by being able to practice on a non-randomised level set, it gives less-scrupulous high-score chasers a leg up on their honest competition.
Used in good faith, though, it's a fun little tool. And, short of an official, leaderboard skipping alternative, it's the only way you'll be able to create a special campaign challenge between you and your friends.