BETONBOX is a free offline drum machine / beat maker for Android with a brutalist concrete visual theme. All sounds are synthesized in code with the Web Audio API — there are no sample files and no server. Features: a 16-step (and odd-meter 9/8, 7/8, 5/8, 6/8) drum grid with 10 channels including Turkish darbuka (dum/tek), per-track volume, pan, tune, mute, solo and lock; two drum kits (acoustic-style and 808); a random beat generator with 17 groove styles (house, boom bap, trap, breaks, funk, DnB, reggaeton, garage, dubstep, rock, latin, and Turkish çiftetelli, düyek, halay, maksum, malfuf, roman); Euclidean rhythm generator; a "similar variation" mutation button; a genre generator that builds a full song; an EXPAND arranger that derives intro/build/riser/drop/breakdown/outro sections; up to 16 pattern banks and a 24-slot song chain; master FX (reverb, delay, drive, tone, vibrato, humanize, sidechain compression) with a compressor and limiter; tap tempo, swing, undo/redo; save and load named projects; and WAV export of the finished beat which can be shared to other apps. The app is completely FREE: there are NO ads, NO subscriptions, NO in-app purchases and NO user accounts. The interface is English only. It runs fully offline and in landscape orientation. The only permission requested is INTERNET (standard for the WebView shell; the app does not require a connection to work).