CanJS vs Ractive.js

Update of single element, no diff like react.

CanJS has an easy to learn syntax.

Ractive fully supports a templating language. To be more precise, views are written with a variant of Mustache, which is also extended to support inline JavaScript expressions. Soon it will be able to support other templating languages.

Ractive has a concept of proxy events, which translate a user action (e.g. a mouseclick) defined via an event directive into an intention (e.g. 'select this option'). This allows you to handle user interaction in a readable, declarative fashion.
on-click='activate'
with arguments:
on-click = 'activate: {{a}}, {{b}}'
It's activate (and not click, nor your function name) that is the name of the handler event that will be fired for any registered handlers created via
ractive.on('activate', your_handler)
ractive.on('activate', your_another_handler)

Of course, Ractive also supports method calls like on-click='toggle(foo)'

Two-way binding can be turned off by those that are concerned it may be a source of bugs.

They have a great interactive tutorial which makes the learning process easy peasy. You will get into it within a couple of minutes.

Instead of relying on the DOM, Ractive implements a virtual DOM from scratch, allowing it to calculate precisely what needs to be patched during the next screen refresh. This is orders of magnitude faster than fiddling with the DOM itself.