Betafish.js, also referred to as Chess AI, is a specialized Artificial Intelligence system with a specific focus on the game of chess. It provides an interactive chess-playing environment, with a broad array of configurable in-game settings.

It allows users to copy the FEN (ForsythEdwards Notation), a standard notation for describing a particular board position of a chess game, and set the same too.

The Reset functionality can swiftly reload the board to the starting position or remove the changes that have been applied. It provides an 'AI Move' feature, where the AI calculates and makes a move on behalf of the user, facilitating users to study the game from an AI perspective.

Notably, the game also includes a 'Take Back' feature, permitting you to roll back your move, and learn from the potential strategic errors. Another standout feature is its ability to flip the board.

This attribute provides the convenience to switch the perspective of the game at any moment. You can also manipulate the AIs 'thinking time', translating to the time the AI takes for calculating and making its move.

This tool is flexible, as you need to determine the duration of time the AI needs for its move from a choice of predefined options. Lastly, the source code of Betafish.js, created by a developer named Gavin, is made available publicly and can be found on GitHub, allowing developers to study, modify, or make contributions to the tool.

In summary, Betafish.js, offers a comprehensive platform for learning and playing chess with the assistance of AI, while also serving as a valuable resource for coding enthusiasts examining the underpinnings of AI in game theory.