Ask HN: How to start a company with an open source alternative of a popular SaaS

Hey HN. Let's say I have built an open-source alternative of a popular SaaS product. The product itself is quite well-known and widely used. For this example, let's say it's Notion. How can I actually start a company around it? The software I built has the following qualities:

- The output (as in what you actually build with the product, in this case, Notion pages) is of VERY similar quality to Notion. For instance, if you showed it some people, they would be immediately sure that it was built using Notion.

- The method of creating the output is completely different. In the case of my open-source software, the approach is local and file-driven, vs using a clunky web app.

- I want to fully open-source the software on GitHub once it is complete, or at least close to complete.

- In some cases, the output can be more flexible and better in performance.

Please note, it's not a Notion alternative, but it makes explaining easier. What would you do here? How do I actually start building a business around this?