Weighing in at 5kb minified + gzipped, Moon is one of the lightest libraries out there.
Moon uses a fast Virtual DOM, and can rerender the DOM efficiently, only updating nodes where changes were made.
Moon's simple API makes it easy to learn, you can get going in no time, just include the script!
<div id='app'>
<h1>{{msg}}</h1>
<input type='text' m-model='msg'/>
</div>var app = new Moon({
el: '#app',
data: {
msg: 'Hello Moon!'
}
});