If you are into Open Sources, you can use penpot https://penpot.app/, it's really good apps for designing UI even in its alpha version. For the design framework, I recommend start learning Jetpack Compose, its really good and potentially be used in multiplatform like flutter but with kotlin power.
From what i know, no it is proprietary. Unlike your code which is BSD licensed it can't be studied, modified, inspected and shared etc. Read more about free software, it is free as in free beer and not free as in freedom.
Sorry I assumed you knew about Free Software since you used BSD license for your code.
P.s. there is also other alternative open source and free software tool called Pen Pot which unlike figma I can self host too.
You could use something like draw.io which is free.
I just found penpot.app , but don't know how good it is.
Then there's Figma, but that is free as in beer, not as in speech.
Since the linked page is full of basically useless marketing, and I just wanted to know if this was Inkscape for workgroups, here's a link to the more informative page on the site:
This is seriously legit. Great job! Are you willing to create a component library of all this for Penpot?
When we developed Penpot (penpot.app) as an open source project that would compete with all of the tools listed here, we thought that a self-hosted open source design & prototyping platform could actually make a lot of sense. Not only to integrate it with other tools in your pipeline but for the sake of privacy and security. We just released our alpha but we are seeing tens of thousands of self-managed Penpot deployments...
I'm not going to go as far as to say Penpot is right now the best tool out there, because it's not, but if you value open source, SVG and cross-functional teams, I think you're going to like what we developed already.