Bootstrap is the seventh-most-starred project on GitHub, with more than 142,000 stars, behind freeCodeCamp (almost 312,000 stars) and marginally behind Vue.js framework. According to Alexa Rank, Bootstrap is in the top-2000 in the USA while vuejs.org is in the top-7000 in the USA.
Mark Otto announced Bootstrap 4 on October 29, 2014. The first alpha version of Bootstrap 4 was released on August 19, 2015. The first beta version was released on 10 August 2017. Mark suspended work on Bootstrap 3 on September 6, 2016, to free up time to work on Bootstrap 4. Bootstrap 4 was finalized on January 18, 2018.
Significant changes include:
Major rewrite of the code
Replacing Less with Sass
Addition of Reboot, a collection of element-specific CSS changes in a single file, based on Normalize
Dropping support for IE8, IE9,[contradictory] and iOS 6
CSS Flexible Box support
Adding navigation customization options
Adding responsive spacing and sizing utilities
Switching from the pixels unit in CSS to root ems
Increasing global font size from 14px to 16px
Dropping the panel, thumbnail, pager, and well components
Dropping the Glyphicons icon font
Huge number[quantify] of utility classes
Improved form styling, buttons, drop-down menus, media objects and image classes
Bootstrap 4 supports the latest versions of the Google Chrome, Firefox, Internet Explorer, Opera, and Safari (except on Windows). It additionally supports back to IE9[contradictory] and the latest Firefox Extended Support Release (ESR).
Bootstrap 5 Alpha
Bootstrap 5 Alpha was officially released on 16 Jun 2020, although an experimental version of the package, created by Material Design for Bootstrap based on a developer version of the Alpha already surfaced the web weeks before.
Version 5 Alpha is currently the latest version of the package.
Major changes include:
Rewriting the grid to support columns placed outside of rows and responsive gutters
Migrating the documentation from Jekyll to Hugo
Dropping support for IE10 and IE11
Moving testing infrastructure from QUnit to Jasmine
Adding custom set of SVG icons
Adding CSS custom properties
Enhanced grid system
Improved customizing docs
Changes that are coming soon:
Implementing an offcanvas menu
Changes that are being evaluated:
Sass module system
Increased usage of CSS custom properties
Embedding SVGs in HTML instead of CSS