UI Widget & Component Toolkits

On Web Platform: ¹

• Kendo UI for jQuery [free to $]
• Materialize
• Office UI Fabric
• Semantic UI
• UiKit
• Webix [$]

React Specific, On Web Platform:

• Ant Design
• Material ui
• Semantic-UI-React
• ExtReact [$]
• Fabric

Native Desktop/Laptop/Netbook Apps via Web Platform (i.e. used with NW.js and Electron):

• Photon
• React UI Components for OS X El Capitan and Windows 10

ADVICE:

¹ If you need a basic set of UI Widgets/Components start with Semantic UI. If you are building something that needs a grid, spreadsheet, or pivot grid you'll have to look at Kendo UI or Webix. Keep in mind that most of these solutions still require jQuery.