Base UI Sketch Framework - Huge set of everything you need to design and prototype
Vidrio - Holographic screencasting app for Mac. Free for COVID-19
UiSketcher - Easily sketch user interface with your pen-enabled device!
Scrimba - Interactive coding screencasts created in an instant
Remake - A way to make web apps with just HTML & CSS
GoRails - Ruby on Rails screencasts for Web Developers