VSCode

What it's made out of

• The text editor is apparently built on top of Monaco Editor.

• The desktop app is built with Electron.js

• The terminal is built on top of xterm.js

• I think they invented, but at least they popularized the LSP (Language Server Protocol) abstraction.

• I think they invented, but at least they popularized the DAP (Debugger Adapter Protocol) abstraction.

• The syntax highlighting and snippets appear to be inspired from and/or utilizing the underlying engines of TextMate