This is a list of unofficial, deadline-less (hence not searchable) bounties offered by users on various challenges on the main site.
Disclaimer: There is no guarantee that the user will award the bounty for you in case you fulfill its requirement. Especially if the user isn't an active member anymore. The only guarantee is his/her written word.
- You can add a missing entry to one of the lists. If the bounty offerer has been seen in the past 60 days (based on his/her profile page) choose the first (active members) list otherwise the second (passive members) list.
- If a bounty is awarded delete it from its list.
- If the offerer of a bounty in the active list become passive move the entry to do passive list.
- An entry can be moved back to the active list from the passive one only by the offerer (to decrease maintenance work).
Offered bounties from active members (sorted by amount):
- 1750 reputation (500 from GentlePurpleRain,
500 from Alconja, 500 from question_asker, 250 from Z Dailey)
- Unsolved Mysteries: Kryptos - provide a credible solution for Part 4
- 1000 reputation (500 from GentlePurpleRain
and 500 from Alconja)
- Unsolved Mysteries: Magic Square of Squares - provide a valid solution or prove that no solution exists
500 reputation from ghosts_in_the_code
- Variant of lion and 100 zebras - submit a formal proof that solves the puzzle either way
- Rigged casino that prevents pairs - do better than 17 (250 rep for proving 17 optimal)
- Maximize 'chains' in a Sudoku - do better than 27 (250 rep for proving 27 optimal)
500 reputation from Rewan Demontay
- Find My Mission For Me - For solving my nearly three-year-old puzzle.
Offered bounties from passive members (sorted by amount):
- 200 reputation from Anachor
- Nine gangsters and a gold bar - provide a full proof that 17 pieces cannot be achieved (or a solution with 17 pieces)
P.S. This practice is followed on Code Golf SE and was approved on Puzzling Meta also (6 upvotes, no downvotes on @xnor 's answer as of today).