Openwrt
The OpenWrt project is a Linux operating system targeting embedded devices. OpenWrt is not a single, fixed firmware; instead, it provides a fully writable file system with package management capabilities. This allows you to break free from the application scope and configurations provided by vendors, and customize your device by installing packages suited for any application.
For developers, OpenWrt serves as a framework for building applications without the need to construct a complete firmware. For general users, it means having full customization capabilities, enabling the device to be used in unexpected and innovative ways.