Starting point for me was to send notifications from my IRC bouncer to my workstations and phone (which now works, yay!) but has extended to common purpose system. For example, if you are running long tasks on your server and want to get notify to you phone when its done, just do simple curl command after && !
Brief intro to get started and running server can be found here: http://lotsof.coffee/
All of this is open source and here comes the links:
server - https://github.com/vhakulinen/push-server
android app - https://github.com/vhakulinen/push-tool-android
linux desktop client - https://github.com/vhakulinen/push-notify-daemon
I've also been experimenting with the reddit's api to get notifications when there is new messages in inbox but that's not ready yet.
Oh, and please don't crash the server if you find bugs, open up an issue on github :)