Unlicensed Nintendo Entertainment System (NES) games are titles released without Nintendo's official approval or Seal of Quality (SOQ), often bypassing the company's 10NES lockout chip that control third-party game distribution. Many of these games were developed by companies like Tengen (a subsidiary of Atari), Color Dreams, Wisdom Tree, and Camerica, using alternative methods such as voltage spikes or custom chips to run on NES hardware. Tengen's Tetris is one of the most infamous unlicensed releases, sparking legal battles with Nintendo. Other unlicensed titles include unauthorized arcade conversions like Ms. Pac-Man. Some unlicensed publishers produced gold or silver cartridges with a switch to enhance compatibility. While often criticized for inconsistent quality, these games remain a fascinating part of NES history, showcasing the efforts of developers who worked outside Nintendo's strict licensing policies.