This article on CMS Critic explains it all.
This is version 1 of their charter: https://wordpress.org/news/files/2024/02/Open-Website-Alliance-Charter.pdf
The Alliance is founded to facilitate collaboration between Content Management Open Source
Projects, in order to further education about and advocacy of open source benefits and
principles. The Alliance’s members seek to promote and defend the rights of open source
projects and ultimately aspire to create a better web.
Scroll down to Appendix 1 to see the manifesto.