Just released https://github.com/comfy/comfy-bootstrap-form

It’s a form builder that extends default ActionView::Helpers::FormBuilder

So it’s a simple drop-in as it matches API of existing Rails form helpers.

If you need forms that are rendered with Bootstrap 4 (final) markup, this will save you a ton of time.

Supports Rails 5.0, 5.1 and 5.2 and wraps both form_with and form_for

Check it out.