Findings:

• RSA Secret Key Challenge
• Secret Me-Meta-Node Challenge
• Secret Santa Summer Nodeshell Challenge 2011
• challenge
• Pepsi Challenge
• Challenge of the Future
• Real World Road Rules Challenge
• Challenge a stupid patent
• The Saltine Challenge
• 13 challenges for the 13th generation
• Nodeshell Challenge
• University Challenge
• Agnosticism is the greatest intellectual challenge
• Christian challenge
• The Cheap Beer Challenge
• Scrapheap Challenge
• Minerva challenges Arachne
• BT Global Challenge
• Front Page Challenge
• Simon Singh's Code Book Cipher Challenge Cracked
• The challenge we face
• Reading Between the Lines: Lessons from the SDMI Challenge
• 24 challenge
• Daz Doorstep Challenge
• voluntary challenges in Nethack and Slash'Em
• The Great E2 Fin de Siecle Fiction Challenge
• European Soccer Challenge
• The 2-sentence Fin de Siecle Fiction Challenge Entry
• Learning Machine Challenge
• The 1-sentence Fin de Siecle Fiction Challenge Entry
• Fiction challenge results
• Challenge of Nexar
• Triangle Challenge
• Triangle Challenge Solution
• The Long Island Challenge
• Fed Challenge
• ECCp-109 Challenge
• Challenge Coin
• Chip's Challenge
• Ferrari F355 Challenge
• American Solar Challenge
• Freedom's Challenge
• James Randi Paranormal Challenge
• Three Peaks Challenge
• BOC challenge
• Challenge for Change
• Full Metal Challenge
• Cheesily Cheerful Chart Challenge
• The Lyme Park Downhill Challenge
• Most Extreme Elimination Challenge
• E2verse Valentines Challenge (collaboration)
• challenge response
• F1 Career Challenge
• The 99p Challenge
• DARPA grand challenge
• Challenge everything
• E2verse previous challenge (collaboration)
• Ivan's challenge
• Three Pint Challenge
• The Mentos Challenge
• wertperch's nodeshell challenge (document)
• Puzzle Quest: Challenge of the Warlords
• The Stephen King Challenge
• Harry Potter Interactive DVD Game: Hogwarts Challenge
• Millennium Challenge 2002
• THE IRON NODER CHALLENGE
• The Notebook Challenge
• Clomid challenge
• THE IRON NODER CHALLENGE 2: ELECTRIC BOOGALOO
• The Nuzlocke challenge
• THE IRON NODER CHALLENGE 3: THIS TIME IT'S MARTENSITIC
• "So?" is a challenge
• THE IRON NODER CHALLENGE 4: FERRASSIC PARK
• The challenge of writing a meaningful free-form poem using only two letter words
• THE IRON NODER CHALLENGE 5: THE FERROUS FRONTIER
• Sahara's Math Challenge # 1
• Noah's Ark challenge
• a partner who challenges you
• THE IRON NODER CHALLENGE 6: RUST NEVER SLEEPS
• The 2013 IRON NODER CHALLENGE (document)
• THE IRON NODER CHALLENGE 7: NODE HARDER WITH A VENGEANCE
• Up for a challenge?
• THE IRON NODER CHALLENGE 8: RUST IS FOR THE WEAK
• THE IRON NODER CHALLENGE: 9 FAST 9 FERROUS
• October Skeleton Challenge
• Ice bucket challenge
• THE IRON NODER CHALLENGE XII: WE'LL RUST WHEN WE'RE DEAD
• even if you fall from an impossible challenge,
• where you see mysteries, i see challenges
• "Age by age" reading challenge
• A Challenge is Issued
• Congratulations, you are about to experience a profound challenge
• Keyboards in a computer lab with very sticky keys that make you
• key sharing
• public key cryptography
• private key cryptography
• private key
• public key
• beanie key
• musical key
• any key
• Key West
• key
• key grip
• Press any key to continue
• The Key of Solomon the King
• Songs in the Key of Springfield
• Songs in the Key of X
• option key
• Key Caps
• Francis Scott Key
• binded key
• Spare Key Savior
• Key tone
• vi keys
• Key Club
• chroma key
• Communication is key.
• backspace key
• CD Key
• key light
• Public Key Infrastructure
• Don't lock your keys in your car
• drum key
• Magic SysRq Key
• function keys
• Make your keyboard's "Windows Keys" into "Super" shift keys for (X)Emacs
• What your keyboard's "Windows keys" do in Windows
• Anonymous Diffie-Hellman Key Exchange
• Win Key
• Key The Metal Idol
• clover key
• command key
• feature key
• flower key
• pretzel key
• propeller key
• compose key
• church key
• cEvin Key
• Enochian key
• Tab Key
• The Golden Key
• The Golden Key: Part 2
• The Golden Key: Part 3
• The Golden Key: Part 4
• I HAVE NO CAPS LOCK KEY AND I MUST NOT SHOUT
• Key lime pie
• Science and Health with Key to the Scriptures
• Key 23
• Boss key
• Special Alt key characters & accents
• I'm starting to think the secret is to NOT be rich and prosperous. To be 'unsuccessful' (depending on who you ask)
• Wandering about with keys dangling from an oversized shoelace around your neck
• Where do they keep the car keys when they transport cars?
• windows key
• finding the key
• key bindings
• Key Martin
• Frisbee is the key to happiness
• Key Fob
• the key commands all emacs users should know

If you Log in you could create a "Secret Key Challenge" node. If you don't already have an account, you can register here.