UI-framework for prototyping mobile apps and websites?

Question

Mobile development

Hello!
The framework must meet the following conditions:
1. Sufficiently developed and popular.
2. Contains css and possibly js components (only components, MVC support is not needed).
3. Desirable Less for css preprocessing.
4. There are themes for the respective mobile platforms.
5. Free :-)
An analogue for desktop sites - Bootstrap. Contains ready-made css-components (grid, form elements, text, etc.) and js-components (modal windows, tooltips, etc.).
Something more or less suitable: Ratchet, ChocolateChip. But it needs to be better.