The best replacement for bootstrap 3 is foundation 5.

The best alternatives to bootstrap 3 are rated as following:
★★★★★  foundation 5
★★★  jquery mobile
★★★  zurb foundation 5
★  topcoat
★  foundation 4

Your alternative for bootstrap 3 is not listed? Suggest!
Speaking about bootstrap 3, one probably shouldn't forget about less.

Other search terms related to bootstrap 3 and their ratings are:
★★★★★ less
★★★★★ rails 4
★★★★ sass
★★★★ datatables
★★★ jquery ui
★★★ angularjs
★ mvc 4
★ responsive
★ font awesome
yii
You have in mind a companion for bootstrap 3 and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of bootstrap 3 in all years. Click on graph for more.
bootstrap 3
foundation 5
jquery mobile