The best open source alternative to Kendo UI is UIkit. If that doesn't suit you, our users have ranked more than 10 alternatives to Kendo UI and 16 is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Kendo UI are Semantic UI (Free, Open Source), jQuery UI (Free, Open Source), Webix UI (Paid, Open Source) and DevExtreme (Free Personal, Open Source).
Pixel Lite Bootstrap 4 UI Kit is a beautifully crafted UI Kit based on Bootstrap 4 Components. This theme was built following Bootstrap's methodologies by the heart. It has 100 components, 3 plugins and 3 example pages.
Kube is one of the world's most advanced and flexible frameworks. Kube helps you spend less time on routine tasks and more time creating amazing products. Focus on success, and Kube will cover the technology behind it.