Abacus

Abacus — a working soroban. Slide the beads, read the value in Arabic and Roman numerals, and learn bead arithmetic step by step.

A clean, fast, single-file browser app. No account, no ads, no tracking, works offline once loaded. Keyboard and touch friendly.

Buy once for $1 to download the standalone build and support development. Made by a civil engineer who builds games and simulations on the side; more at boardgaminghub.com.