In the B2B SaaS world, it means they're signing up new customers (e.g. including some who might have well known logos).

Outside of bizdev brotalk, isn't that called "new clients"?

not just new clients, recognizable clients who are willing to be associated with you

Its a pretty common KPI for B2B companies.

It makes sense if you take in context that Flux, the most visible and well-known product of Weaveworks, is a donated CNCF open source project, and that companies like Microsoft, VMWare, AWS – can all engage with it directly, or by forking, or by building support for it directly into their own products.

How do you place a value on Microsoft building Flux into Azure Arc? I know it isn't worth $0 but do they actually need a contract with anybody (at Flux or Weaveworks) in order to go on doing that - no. They don't need one.