Notpron

[3] Regarded as one of the first of the online puzzle game genre, Notpron follows a standard puzzle game layout, where the player is presented with a webpage containing a riddle and must find the answer to the riddle in order to proceed to the next webpage.

Each level answer or solution is unique, often requiring specific skills such as decoding ciphers, image editing, musical knowledge, and formerly, remote viewing.

Inspired by a game he played online entitled "This is not Porn", Münnich created the first five levels in 2004, put them in a folder temporarily called "notpron", and posted it on his website.

Soon thousands of people showed up to play the game and, by then, it was too late to change the name.

[6] Kashann Kilson of Inverse called the game "the perfect combination of a logic puzzle and an online scavenger hunt.

Notpron's first level, which requires the player to click the door to proceed. Subsequent levels increase in difficulty, requiring the player to perform various tasks such as modifying the URL, editing images, and viewing the page source code for clues.