Ember.js
Convention-over-configuration JS framework — "Ruby on Rails for frontend". Yehuda Katz + Tom Dale, 2011. Used by LinkedIn, Discourse, Apple Music web.
Strong opinions about structure: Router, Routes, Models (Ember Data), Components. Unlike React/Vue, Ember provides a whole stack including routing and data out of the box. Less popular since ~2018 (Vue/React sucked the oxygen out). Ember Octane (2019) modernization. Tom Dale now works on Mainstay; Yehuda Katz on Tangle. Discourse is the biggest open source consumer — still drives Ember development.