Your everywhere Studio by Spotify

 https://www.soundtrap.com/

Online audio editor (DAW?) from spotify

tiptap – a renderless rich-text editor for Vue.js

https://tiptap.scrumpy.io/
Kinda like tinyMCE, but for vue.

Editor.js Next generation block styled editor. Free. Use for pleasure.

https://editorjs.io/
Interesting on-page javascript editor.

The quest for sustainable free/libre non-linear video editors

http://libregraphicsworld.org/blog/entry/the-quest-for-sustainable-free-libre-non-linear-video-editors
Survey of the major open source non-linear video editors, their state of development and economic models.

A hackable text editor for the 21st Century

https://atom.io/
Interesting opensource cross-platform text editor. Notable for its plug-ins. 

Sigil is a multi-platform EPUB ebook Editor

https://sigil-ebook.com/
An opensource, multi-platform ebook editor.