Free Bootstrap WYSIWYG Editor [on hold]

Is there any site / software that:

Lets you design / mockup visually (WYSIWYG). Ie: Drag-and-dop components
Is free and/or open source
Works with Bootstrap
Lets you edit code
Has no branding (Some softwares add their brandig for free users)
Lets you test the design for desktop, mobile, etc.

Tags: UX Stack Exchange