This looks identical to the Sencha products [0]. Especially, their ExtJs framework [1].
Both the name and even their examples [2] look practically like copies. Although, ExtJs does seem more fleshed out and way more full fledged [3]. They seem to have bindings with other frameworks too, like React and Angular [4].
The ExtJs framework started as an open source project ages ago. Is this some kind of a fork from then?
Ext.NET includes Ext JS (currently, v7.1.0) as its client-side component UI. The new Ext.NET 7.0 release provides 100% coverage of all Sencha Ext JS components to use in ASP.NET Core apps, such as Razor Pages or MVC.
Release info: https://ext.net/download/#version