App

Reckless Amphitheater

v1.0.0

A free chess GUI and engine host: play against an engine, have several analyse a position at once, and run matches and tournaments between them with clocks, opening books, pondering, adjudication and PGN. Five chess engines come with it, ready to play the moment you open it.

The Reckless Amphitheater window during an engine match.

Download

Free, for any use, on as many computers as you like, for Windows, macOS and Linux. The code is public to read, though it is not open source; the five engines it carries are.

Download version 1.0.0

To uninstall it: on Windows, Reckless Amphitheater in Settings > Apps; on a Mac, Uninstall Reckless Amphitheater in /Applications/Reckless Technology, which leaves the other Reckless apps alone; on Linux, sudo apt remove reckless-amphitheater, or delete the unpacked folder.

The five engines it carries

Every installer carries these as separate programs, which the host talks to over UCI as it would any other engine. They appear in the engine list the first time you open it, so there is nothing to set up. Each is open source under the GPL, with its own page here and its source on GitHub.

Pawnstar — C++: bitboards, a Lazy SMP alpha-beta search and an NNUE evaluation
Zenith — C17: small and simple by design, with a network it trains itself - the strongest of the five
Pawnstar-Go — Go: hand-written AVX2 and NEON kernels for the network
Pawnstar-RS — Rust: bit-exact with the C++, every node count and score identical
Stoopid Chess — C#: first written in 2009, rebuilt in 2026 for .NET 10

On macOS the host is universal; the five engines are built for Apple silicon.

What it does

The window gives the board the room and puts everything else around it: the moves in SAN down one column, the two players with their clocks (the running one lit amber) and the game’s card between them, and across the foot the analysis, the evaluation graph and the engine log.

The Reckless Amphitheater window during an engine match: the board, the moves, both clocks, the analysis of two engines, the evaluation graph and the engine log. — The window during a match. Scores are always from White’s side, whichever engine reported them.

Playing a game

Move a piece by clicking it and its square, or by dragging; the legal squares are marked as you go, and a promotion offers a picker. Game > New game sets up who plays each colour — you, or any engine on the list — the time control, and the opening to start from. Flip turns the board round, and the plates under the card step through the moves.

Edit > Set up position builds a position square by square when you would rather start from one of your own.

The position editor: a board being set up square by square, with the castling rights and the side to move beside it. — Setting up a position.

The engines

Five engines come with the host and appear in the list the first time it opens, each set to one thread and a 64 MB hash. Engines > Engines adds any other UCI engine on your computer, sets its options and takes one away; a new release of the host moves the five on and leaves your own settings alone, and one you remove stays removed.

The engine list: the five bundled engines with their options, and the buttons that add another. — The engine list, with the five that come with it.

Analysis

Analyse sets engines thinking about the position on the board and keeps them on it as you move through the game: each one’s depth, speed and best lines appear in the analysis panel, and the evaluation graph draws the game as they see it. Game > Analyse the game goes over a whole game move by move and writes the scores, the engine’s lines and NAGs back into it.

Matches and tournaments

Match and Tournament play engines against each other: a round robin with as many games at a time as you have cores, clocks with an increment, an opening book or a file of openings to start each game from, pondering, and adjudication when a game is plainly decided. The standings show points, the score, the win-draw-loss count, Sonneborn-Berger and the crosstable, with an Elo difference and its margin.

The new tournament dialog: the engines chosen, the time control, the openings, the number of games and the concurrency. — Setting up a tournament.

Standings and crosstable: four engines with their points, games, score, wins, draws, losses and Sonneborn-Berger, and the crosstable beneath. — The standings and crosstable as a tournament runs.

Openings and books

File > Open book shows a Polyglot or PGN book’s moves beside the board and faintly on it; Zenith’s own book is built in. File > Make book from games turns a PGN file, a folder of them or a zip archive into a Polyglot book, each move weighted by the games that play it. Games are read and written as PGN, variations, comments and NAGs included.

The command line

amphitheater-cli installs beside the window and runs the same matches, tournaments, analysis and perft from a terminal, so a long tournament needs no window open. The tournament dialog writes its arguments, so the two never disagree on an option.

Updates

Amphitheater asks this website whether a newer version is out, and tells you in the window when one is. It never downloads or installs anything itself, and the request carries the version you have and nothing about you or your computer (privacy).