1. Syntax and Configuration: Grunt uses a configuration file where you define tasks using a JSON format, Sagui utilizes a configuration file similar to Grunt but with a simplified and more concise syntax, while Webpack uses a JavaScript file to define its configuration.
2. Bundle Optimization: Grunt and Sagui focus on task automation and build processes, while Webpack is primarily a module bundler that excels in optimizing and bundling assets for production.
3. Code Splitting: Webpack has built-in support for code splitting, allowing you to split your code into multiple bundles that can be loaded on demand, a feature not directly supported by Grunt or Sagui.
4. Hot Module Replacement (HMR): Webpack offers Hot Module Replacement out of the box, enabling modules to be replaced without a full page refresh during development, a functionality not natively available in Grunt or Sagui.
5. Plugin Ecosystem: Webpack has a vast and active community-driven plugin ecosystem that extends its functionality, while Grunt and Sagui have fewer plugins available due to their focus on task running and build processes.
6. Tree Shaking: Webpack has built-in tree shaking capabilities, allowing it to eliminate dead code and optimize bundle size, a feature not present in Grunt or Sagui.

In Summary, the key differences between Grunt, Sagui, and Webpack lie in their syntax and configuration setups, bundle optimization approaches, support for code splitting, Hot Module Replacement functionality, plugin ecosystems, and tree shaking capabilities.