Open a view or form in a Bootstrap popup like the we use on this site. Go ahead, check it out. Click the login link at the top of the page. Not only can you insert a form or view in a modal, but you can use any shortcode you would like from any plugin that uses regular WordPress shortcodes.
Inserting the link to open the modal is a simple as inserting a shortcode on your page. Insert [frmmodal type="formidable" id=25 label="Click me" class="extra classes here"] for a form or [frmmodal type="view" id=25 label="Click me"] for a view.
Insert the login form shortcode and any other shortcodes with [frmmodal label="Click me" type="frm-login" label_log_in="Log in"]. Replace "frm-login" with the name of your shortcode, and add any parameters you would like passed through. "label_log_in" is an example of using a parameter from the frm-login shortcode inside the frmmodal shortcode. Smooth sailing!
Additional shortcodes, such as the frm-field-value shortcode, can be inserted in a modal like this: [frmmodal type="frm-field-value" field_id="x" entry="12345"]