Blazor - An experimental web UI framework using C#/Razor and HTML, running in the browser via WebAssembly
Bizness Apps - Create your own app or become a reseller and build apps for others
Angular.io - Angular is a JavaScript web framework for creating single-page web applications. The code is free to use and available as open source. It is further maintained and heavily used by Google and by lots of other developers around the world.
Siberian CMS - Siberian is an Open-Source and Free App Maker. Unlimited Push Notifications. Unlimited features. Fully Customizable. Download it and build your own app now!
HTML5 - 5th major revision of the core language of the World Wide Web
Dropsource - Mobile development platform for building native iOS & Android apps