Build anything. Sell anything. Just don't sell Eustress.

Two licenses. One line between them.

Every file in the repository ships under PolyForm Shield 1.0.0. That license is free, permanent, and requires no signup, no key, and no conversation with us.

It grants you the right to use, run, modify, fork, and distribute Eustress for any purpose except one: providing a product that competes with Eustress itself.

If you need that one thing, or if your legal team needs conventional commercial terms, the Eustress Commercial License exists for exactly that.

What the Shield license gives you, free, forever.

• Build and sell games, simulations, digital twins, training environments, and visualizations made with Eustress. Keep 100% of the revenue. No royalty, no platform tax, no threshold.
• Use it in production, at a company of any size, without asking.
• Modify the source, keep your changes private or publish them.
• Fork it. If Eustress vanished tomorrow, your fork would still compile and still ship.
• Academic work, research, evaluation, personal projects: all covered.

The free tier is the whole engine, not a crippled demo. The thing we open is the thing we run.

The one thing it does not give you.

You may not take Eustress and offer it, a fork of it, or a substantially similar engine, editor, or simulation platform as a product of your own, hosted or distributed, paid or free.

That is the entire restriction. It is called a shield for a reason: it protects the project from being strip-mined by a larger competitor, so it can stay free for everyone actually building with it.

Your game is not a competing product. Your digital twin is not a competing product. Your consulting work built on Eustress is not a competing product. A rebranded Eustress-as-a-service is.

The commercial license.

If your use crosses that line, or your organization needs terms the Shield license cannot offer, we sell a commercial license, negotiated per organization.

• Rights beyond the noncompete, where we choose to grant them.
• A perpetual grant for a specified version range, independent of the public repo.
• Warranties, indemnification, and support SLAs for procurement and legal teams.
• Pricing scales with the rights granted, not with revenue the Shield license already permits.

No surprise invoice. If you are building with Eustress rather than building a substitute for it, you will never need this page's second half.

Why not plain open source?

We tried the pure route in our heads a hundred times. The failure mode is always the same: a hyperscaler forks the engine, outspends the community, and the original starves.

PolyForm Shield is the honest middle. The source is fully readable, forkable, and free for builders, and the one entity it says no to is a competitor reselling our own engine against us.

Commercial revenue from that line flows back into the platform economy that pays builders. We win when builders win. That is the only deal that holds.

Read it for yourself.

Do not take our summary as the contract. The LICENSE file is the contract, and PolyForm publishes the canonical text.

If you are planning something big, or you are not sure which side of the line you are on, ask us. The answer is usually: you are fine.

Commercial and licensing questions: licensing@eustress.dev