I have hand picked these tools. Each tool is usable as a drag and drop bootstrap builder. Some are of freemium model which means they are free to use but has limitations.
Layoutit: Clean drag and drop bootstrap theme developer. You should already have some CSS and HTML and responsive design experience to use this tool. FREE.
Eden UI: Minimalist drag and drop boostrap template builder. Loaded with some clean and professional looking web components to quick start template development. Paid. Start at $22 for the builder.
Mobirise: A popular bootstrap website builder. Loaded with a few professional web components. Additional components can be bought from their marketplace. Download for Windows and Mac. Free.
Bootstrap Studio: Desktop APP for designing websites using Bootstrap Framework. Paid. $25 lifetime license.
Brix.io: Some nice and sleek looking web components included in the builder. Paid/Commercial. Starts at $14.95 /month.
Ultimate Blocks: Block based HTML drag and drop, Bootstrap theme builder. Paid / Commercial.License costs $24.
Pinegrow: Powerful drag and drop theme builder that allows you to create themes based on Bootstrap, Foundation or even plain vanilla HTML. Paid / Commercial. License starts from $39.
Jetstrap: Web based responsive Bootstrap interface builder. Paid / Commercial. Starts at $14 for single developer license.
BootGear: Another drag drop Bootstrap theme builder. Not many variations in blocks. Paid/ Commercial. Cost $28 for regular license.
Draggie: Preloaded with 16 Bootstrap themes to chose from. Paid/Commercial. $49 /year license fee.
Pingendo: Comes in 2 varieties – online app and desktop app. The great part is – it is free! So grab it while it is still in beta!
Blocks Bootstrap Builder: Simple drag and drop builder. Loaded with 100+ blocks and 25+ web templates. Pricing starts from $39 for basic license.
Rapid Moon: Fast Bootstrap Interface builder. Web based platform. Signup for their beta testing.
Landing: Drag and Drop Bootstrap based page builder with export / import functionality with 9 Bootstrap templates. Paid / Commercial. License at $14.