Ventute: a business simulator built to replay every run bit for bit

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Ventute is a business simulation platform where users run a company by making decisions while the engine projects what happens next. Its state is never stored directly; instead, every action is recorded as an event and the state is rebuilt by replaying the event log, so identical inputs yield identical outputs. The developer, who built most of the platform alone over the past year, had to control wall-clock time, randomness, iteration order, and floating-point behavior to achieve exact replay. For Monte Carlo forecasting, the hot loop was moved to Rust and exposed to Python via PyO3, enabling true parallel execution while keeping results deterministic. Three reusable components, including the replay kernel, were released as open source on GitHub.

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