One example that I use often — the Photos app on Mac has a built-in editing interface, but also supports extensions that allow third-party apps (e.g. Affinity P

One example that I use often — the Photos app on Mac has a built-in editing interface, but also supports extensions that allow third-party apps (e.g. Affinity Photo and Pixelmator) to take over that whole UI and present their editing UI inside the Photos app.