What is Riot.js?

Clearly exposed in the documentation, Riot was inspired by Facebook's React. Their proposal is to have simple syntax, and to be light - lightness is a bold point to touch, because if the lightness in question is in the performance of the library is a challenge for them to compete with React, mainly due to the best balcony, for me, of Facebook - Virtual DOM.

Riot has Express Binding, which basically stores the expressions created in an array, and each expression has a pointer to the node in the DOM. Obviously discussing about the structure of updating elements in the DOM tree is a matter for another lunch (or post), but it is important to pay attention to this, because what differs from Riot's direct competitor is the componentization structure and Virtual DOM .

And Riot is basically this, a library with simpler syntax than its similar ones, that has a special attention in working with templates and that tried / tries to solve holes of the React.

  

As there are already several libraries / frameworks with similar purpose   (Angular, React, Vue, etc.) what would be the motivations for   choose Riot.js?

This depends on the project, Riot.Js is very light and makes it a lot easier to create a template, now if you need something that needs to work side-by-side with the back-end react would not be a good solution compared to others frameworks

  

Do the "custom tags" they offer do not break web standards?

Edit: Generating new tags leaves the html depedent of the framework, it is impossible to change framework, there is not a default break, but a new implemented pattern.

  

What would be an overview of the library?

Generate template more easily.

and has a good summary of some frameworks here: link material in english