NotPr0n

Notpr0n is an internet puzzle game developed by David Münnich in August of 2004. Notpr0n is one of the oldest, if not the oldest online games of this kind. It features 138 total puzzles with some optional secret levels. David Münnich is also known for developing one of my favorite puzzle exploration games, SupraLand.

To get started with the game, you can begin here.