Dart vs Polymer vs Bootstrap

Bootstrap is a CSS framework with a set of CSS styles for many common use cases and also a set of common elements that have more advanced functionality built with JavaScript.

Polymer has nothing in common with Bootstrap (beside that it is for the web).

Polymer is a framework that is based on some new web standards like custom elements, templates, HTML imports and others and polyfills to make these features available to browsers without native support.While you can build custom elements with JavaScript alone, Polymer builds on top of it to improve the developer experience and saves a lot of boilerplate code and adds features like mustache data binding.

Custom Elements is an emerging web standard that allows to build your own tags like the existing <input> tag or a <video> tag where <your-advanced-tag> hides some more or less complex implementation consisting of HTML, CSS and JS (or Dart). In your HTML you just add <your-advanced-tag> and the page contains the full functionality. Polymer.dart is a Dart port of the Polymer.js framework (for 1.0 it will probably be just a wrapper on top of Polymer.js because Dart VM in Chrome was dropped and building a real Dart implementation doesn't provide much additional value).

While there are already a lot of Polymer elements available, Polymer is just the framework not the elements built on top of it.For more information take a look at http://www.polymer-project.org/

Dart is a language that aims to support developers building complex web applications,but you can also build server or command line applications with Dart (building Android and iOS applications is experimental/work in progress see https://github.com/domokit/sky_sdk)This is great because you can build all parts of a complex client/server app in Dart and probably share a lot of code between client and server.Dart has a VM that allows to run Dart applications on Windows, MacOS, Linux, Android, ...The VM is also already integrated into Dartium (a Chromium derivative) which allows to execute browser applications without a compiling step which leads to great developer experience.