UCThello is a board game using Monte-Carlo Tree Search (MCTS) with UCB (Upper Confidence Bounds) applied to trees (UCT in short) for the computer player AI. The board game used for demonstration purposes of the UCT algorithm is close to a game named Othello depending on selected options. In fact it can be played depending on your configuration following the official tournament rules of the WOF - World Othello Federation - if intended [WOF14]. Other rule settings to play variants are available, too. Per design decision the playing strength is limited for pleasure and fun level. Thus it is kept at a moderate to quite strong level on purpose due to the target environment, device platform, and audience expectations. This is done e.g. by limitation of the maximum AI response time and using a single execution thread for AI only plus just a second independent execution thread for a responsive user interface to avoid battery drains if full CPU and GPU core support would be implemented leading to bad user experience. Other possible but at least currently postponed improvements could be done by simple usage of a well-known and available game opening book. Although such simple modifications could improve the playing strength these features are not implemented in the current version yet. Othello is a derivative of the board game Reversi which can be played by UCThello as well. Reversi is claimed to be invented by either Lewis Waterman or John W. Mollett. Predecessor of Reversi created by Mollett is The game of Annexation, also called Annex back in 19th century.