Bootstrap says that it "helps nerds do awesome stuff on the web".
That's very true. Bootstrap is an entire framework that was developed by Twitter to allow them to quickly and easily create consistent, good-looking, mobile-friendly designs. It worked so well that it's now become an independent project used across the web.
Bootstrap is so popular that Joomla adopted it entirely. There are also a good number of WordPress designers using Bootstrap.
In this blog post, we evaluate 8 free WordPress themes built on Bootstrap.
Recommended: The Bootstrap
The Bootstrap is half-way between a theme and a framework. It has enough design elements that I actually felt comfortable using it for my personal blog at SteveBurge.com. However, for client work, most people would need substantial extra design work.
I found this to be a clean and complete adaptation of Bootstrap to WordPress.
Response is the most popular free Bootstrap based theme for WordPress. Why? Probably because it has the most comprehensive, out-of-the-box design. It has a mobile-friendly slideshow and a wide range of theme customization options. Oddly, Responsive design is one option that is disabled by default when you install Response.
Cyberchimps is the framework underlying the Response theme. The Cyberchimp team have made it available as a separate download.
Voyage is definitely worth considering. It's a good number of theme options, it's (almost) up-to-date and it has been adapted cleanly to WordPress.
Recommended: Roots Theme
Roots Theme is undeniably a framework and will need customizing. It's the first on this list to not be listed on the WordPress theme directory.
I did have some installation problems with theme but was able to resolve theme quickly with the answers on their Google Groups forum. There's an impressive level of activity around this theme.
Along with Response and CyberChimps, this theme is the furthest away from a clean and simple implementation of Bootstrap. They've added a lot of their own work here.
Recommended: WordPress Bootstrap
WordPress Bootstrap is full of customization options and has a very WordPress-friendly adaptation of Bootstrap. Perhaps my favorite feature is that it allows you to automatically apply designs from http://bootswatch.com. This is a slick and clever way to quickly break out of the blue-and-white Bootstrap design that we've seen in all the themes so far.
If you're going to start your journey with WordPress and Bootstrap, you'd be making a good choice by starting with WordPress Bootstrap.
Wordstrap is another Bootstrap theme with a finished design, but it's not the prettiest and its Bootstrap version is out-of-date.
Bootstrap for WordPress
It's hard to recommend this theme because Bootstrap is long way out-of-date and the code is not smoothly adapted to WordPress