Their website is

https://www.avaloniaui.net/

Where did you go?

[Edit] Sorry, I see that you are talking about the "XPF". I didn't use that before.

That's for Avalonia XPF, their product that runs WPF apps on Linux and Mac. Avalonia UI is free and licensed under the MIT license.

There are two Avalonia products: free and open-source Avalonia UI and paid Avalonia XPF. Looks like [1] XPF allows making existing WPF apps cross-platform while Avalonia UI is more for developing from scratch.

[1] https://avaloniaui.net/Blog/migrating-wpf-applications-avalo...

Just to clarify what is what: Avalonia UI is free, what is expensive is their XPF solution, which allows you to get free cross-platform features for your existing WPF app. So this is very much targeted at companies with legacy code that they want to make cross-platform without even more expensive rewriting.

As others have said, this only for a particularly hairy product called XPF, not Avalonia, so the price point is probably warranted, lol. Basically, they remimplemented WPF itself, the whole shebang as far as they could, to make a transition towards cross-platform support. Microsoft never even attempted this. It's for people mainly having a large, legacy WPF product so they probably already are a business and a desperate one at that to look at these fixes.

But if you're making something from scratch, just use the free Avalonia.

By the way, Avalonia also supports NativeAOT, unlike WPF, if used with the compiled bindings feature. Pretty cool!

Used it for a couple of internal applications for a former client, zero cost.