SilverBullet has been designed to be programmable from the ground up. The core of SilverBullet is relatively small, see Architecture.
On top of this core, a lot of functionality is built as Plugs and [Space Lua](Space Lua) scripts. Write a few lines of code as part of your notes to create a custom command, a slash command or page template, and your notes app quickly becomes a tool shaped to your brain.
While not as fundamental in this approach as editors like Emacs, it draws a lot of inspiration from it.
Many people use SilverBullet as a personal application Platform and build remarkable things on top of it.