I highly recommend UIKit [1] for anyone looking to pick a front-end framework. It solved tons of design problems that I faced with Bootstrap. Here are a few —
1) Every class name is prefixed with "uk-": a wise decision to avoid conflicts and make it easy recognise the framework classes.
2) Useful generic classes: UIKit has many helper classes to avoid adding another rule—for removing padding, introducing a small margin, rounding the borders, adding a box shadow.
3) Clean theme: The default UIKit theme looks an order of magnitude better than Bootstrap's.
4) Additional helpful components: Loading spinner, Cards, Notifications, Sortable list. Shipping them by default saves a lot of time in searching and integrating them in your application.
5) Default Icons Support: The icons look clean and beautiful and because they are SVG, they don't require a font file. (Although, requiring Javascript can be turning off for some)
6) Much better components: Try creating an input box with an icon in bootstrap; with UIKit it only takes a little markup.
Whenever I develop with Bootstrap, I have to spend half the time muting the existing styles and introducing new ones. With UIKit, it never felt like a problem.
If he takes a look at v4 beta than ui-kit creator will ask him to look at the next beta. This is an endless cycle. I think he's comparing against 3 which is valid. And from your replies, it looks to me like he's right on all counts.
Unlike Bootstrap (and Foundation), UIKit has no statement about the accessibility of what it provides. Some of its JavaScript includes ARIA attributes but who knows if they did it correctly; adding ARIA wrong can sometimes make sites less accessible than if it wasn't used at all.
UIKit has many CSS classes with hover states but not focus states and it's not easy to add them to classes like .uk-hidden because it's not a direct declaration but relies on a parent class. It lacks an equivalent to Bootstrap's .sr-only (visually hide but expose content to screen readers); you can always add such a class yourself but it makes the UIKit framework incomplete. UIKit makes it harder to make a site accessible than if UIKit was not used.
CSS Frameworks are supposed to make the job easier by taking care of problems you're not even aware of; UIKit fails to do that in this respect.
1) I don't know if that's a wise decision. To me, BS serves as a "base", my custom classes extend and borrow from BS and everything is knitted together.
2) BS 4 added a ton of helper classes, to the point where I find myself using these rather than writing custom CSS.
3) Ultra light font weight, light gray font color, capitalized text might look great, but I prefer better usability. The point with BS (as of my observations that is) has always been to provide a no-bullshit™ style. It doesn't follow trends, it does what's sane.
4) I half-agree. Not sure how useful it is to have "notifications". I personally never needed that and doubt their usability on mostly document oriented websites.
5) BS used to come with icons, but now there are tons of icon sets to choose from. BS is a CSS framework after all.
6) Besides that, what components does UIKit have that BS can't do? Maybe sticky behavior with a delay would be helpful.
BS is 125 KB vs UIKit 256 KB minified though (that's only for CSS), besides all the accessibility issues.
I really liked ui-kit for my website https://www.itnry.com .It just took couple of days of work to get it going. Huge fan of bootstrap too. For backend engineer who hated CSS and front-end, Bootstrap really helped me build good looking ui's at work where instead of plain old Dev JSP
1) Every class name is prefixed with "uk-": a wise decision to avoid conflicts and make it easy recognise the framework classes.
2) Useful generic classes: UIKit has many helper classes to avoid adding another rule—for removing padding, introducing a small margin, rounding the borders, adding a box shadow.
3) Clean theme: The default UIKit theme looks an order of magnitude better than Bootstrap's.
4) Additional helpful components: Loading spinner, Cards, Notifications, Sortable list. Shipping them by default saves a lot of time in searching and integrating them in your application.
5) Default Icons Support: The icons look clean and beautiful and because they are SVG, they don't require a font file. (Although, requiring Javascript can be turning off for some)
6) Much better components: Try creating an input box with an icon in bootstrap; with UIKit it only takes a little markup.
Whenever I develop with Bootstrap, I have to spend half the time muting the existing styles and introducing new ones. With UIKit, it never felt like a problem.
[1]: https://getuikit.com/docs/