Terms of use
Markstrata is free and open source software, released under the MIT licence. The licence is the agreement; this page says what it means in plainer words.
What you may do
Anything the MIT licence allows: use it, install it across your tenant, change it, build something else out of it, at no cost and without asking. The full text ships with the source and is linked at the foot of every page.
The one condition is the licence's own: keep the copyright notice and the licence text with any copy or substantial portion of the software.
What is not promised
The software is provided as is, without warranty of any kind. It is built in evenings and weekends, tested as carefully as one person can manage, and nobody is on call for it.
That matters most where your documents do. Markstrata renders what SharePoint holds and can write back to it when you use its editor, so treat it as you would any other tool with access to your files: try it somewhere that does not matter first, keep version history on, and satisfy yourself it behaves before pointing it at anything you cannot lose.
Deciding to deploy it, and to whom, is your organisation's decision and your organisation's responsibility.
Not a Microsoft product
Markstrata is an independent project. It is not made by, endorsed by, or affiliated with Microsoft. SharePoint, Microsoft 365 and Teams are Microsoft's trademarks, used here only to say what this runs on.
Whether it may be installed in your tenant is your administrator's call, under your own organisation's policies.
Changes
This page changes when the software does. The version you agreed to is the one in the release you installed, and the history of both is public in the repository.