Factorio is not available as a web app but there are a few alternatives that runs in the browser with similar functionality. The best free Online alternative is shapez.io, which is also Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to Factorio and three of them are free and available as a web app so hopefully you can find a suitable replacement. Other interesting free Online alternatives to Factorio are Factory idle and Factorio Calculator.
Shapez.io, open-source and inspired by Factorio, is ideal for casual gamers due to simpler mechanics. It’s web-based, providing fast access, unlike Factorio’s in-depth management. While Factorio supports Mac, Windows, and Linux, shapez.io offers online play and community collaboration.
Factory Idle offers a simpler, online-based experience for factory building enthusiasts compared to the complex, standalone Factorio. With browser support, Factory Idle is more accessible for casual play, while Factorio offers deep strategy, modding, and multiplayer on multiple platforms.
Factorio Calculator is a tool that helps players calculate resource production and consumption in the game Factorio.
It's free and still pretty entertaining.