You can run Virtual wiring on Yúns! Virtual Wiring lets you build home automation systems, bots, monitoring systems with text/email notification (as examples) with a Yún without the need for programming. To build a system, you connect your devices/sensors to the Yun's I/O pins and configure it from web screens. You can build sophisticated systems in minutes.
Virtual Wiring runs on Linux/*nix hosts and it has screens for configuring, monitoring, and modifying whatever systems you build. It's written in the Ruby language, so if you want to do some programming, you can write your own Ruby code (but it's generally not necessary).
Virtual Wiring is described here:
http://www.catalinacomputing.com
There's a HowTo for installing Virtual Wiring on Yúns here:
http://www.catalinacomputing.com/docs/HowTos/HowToInstallVWOnArduinoYun/HowToInstallVWOnArduinoYun
Virtual Wiring is free for non-commercial use, which basically means if you want to build projects without selling them, it's free. You will see the license agreement when you download Virtual Wiring.
Hope this is useful to people!