Scrum is essentially a product development framework. Vima, by contrast, is a framework for NON product development work. From a design philosophy point of view, this is the key difference.
From a practical point of view, the main difference between Vima and Scrum is what the taskboards and artifacts look like. Vima sprint backlogs integrate a weekly calendar, and Vima "team backlogs" look a little bit like a User Story Map with a calendar stuck on the side. This calendar integration is the most visible, obvious difference with Scrum (besides the single Team Lead role) but there are many other differences. For example, almost all the meetings are somewhat different in purpose and structure.
Many Scrum implementations allow for a percentage of unplanned work, but if a substantial amount of the team’s work does not come from a single Product Backlog, Scrum is probably not a good choice.
Before 2020, Scrum was explicitly a product development framework (and before that, a project management framework).
Since 2020 Scrum has aimed to become a more universal method, but is still constrained by some aspects of product development. The current definition is: "Scrum is a lightweight framework that helps people, teams and organizations generate value through adaptive solutions for complex problems."
Based on this definition, we can infer that Scrum is still specifically targeting product development. Besides, team members are still called "developers" and the leadership role is called "Product Owner".
Vima is openly derived from Scrum. We call it a 'fork' of Scrum. When creating Vima, we took all the Scrum patterns we found useful and integrated them into a framework for business teams. Vima co-creators are long-time CSTs - highly respected experts within the Scrum community. We know Scrum well.
We thought deeply about whether these patterns deserved to be called something new. We tried calling it "patterns for Scrum outside of software" for a while. We were not happy with the results, people would ask us to put our thinking more clearly down on paper and they would dismiss our ideas as "just another implementation of Scrum for a specific environment" (which we believe Vima is not)
In short, we think calling Vima a variation or flavor of Scrum would constrain us and make our ideas less heard, besides being incompatible with the definition of Scrum that is defined as immutable. There is no Scrum Master or Product Owner in Vima. There is no Product Backlog in Vima. There is no Sprint Review in Vima... these are big differences!
Scrum is tightly controlled by the original authors. Many good ideas are left out in a pursuit of simplicity. Vima is more prescriptive than Scrum, and bigger (more events and artifacts). We can be more creative and explore more options with Vima and a more prescriptive framework.
Scrum stays at team level. While mainly a team-level framework, Vima integrates concepts from scaling, leadership development and organizational design as part of the framework philosophy and coverage.