"a) Neither the Work nor any of its individual components, in Original or Modified Versions, may be (i) sold by itself; (ii) used for website or app generators; (iii) used to create templates, themes, and plugins for sale."
It doesn't disallow using them for personal or commercial use by developers but I admit that most of what they've done must rely on the Bootstrap APIs so I have doubts there's much that can be copyrighted by them in what's there.
"a) Neither the Work nor any of its individual components, in Original or Modified Versions, may be (i) sold by itself; (ii) used for website or app generators; (iii) used to create templates, themes, and plugins for sale."