Not an app, but an API. And an app on top of that, if desired.

Also there are evergreen interfaces, so to say. An RS232 / RS485 connector that serves 115kbps 8N1 serial interface and runs a VT220-based TUI should still be serviceable 40 years from now (VT220 was released 42 years ago). A now-modern web-based GUI also has a great chance to be serviceable 40 years from now.