TinyMCE
Classic WYSIWYG rich-text editor. Moxiecode (then Ephox, now Tiny Technologies), 2003. Powered WordPress Visual Editor for 15 years. Mainstream for CMS editing.
Plugin ecosystem: image upload, tables, code view, math (MathJax), spell check. WordPress switched to Gutenberg (block editor) in 2018 — TinyMCE lives on in Classic Editor + many legacy WP installations. Competitors: CKEditor (same era, honestly opinion-split), Quill (newer, simpler), Tiptap (modern, headless), Lexical (Meta, modern). Tiny Cloud is the managed service. Pricing: open source + premium plugins + cloud hosting.