Desktop notifications are great for notifying you about long running processes like tests or compiles. But, at work we use Vagrant, so alot of compiles and tests take place inside of a virtual machine. And that makes it a bit tricky to dish out helpful desktop notifications.
Growl is a desktop notification system for Mac and it does two helpful things to make it possible to push notifications from a virtual machine. First, it has a network protocol so you can send notifications via TCP. Second, it advertises the network service via mDNS. Awesome!
Using these two features I wrote cheekh which can send a notification from either the host or guest machine. If no Growl server is found it quickly times-out.
tl;dr you can find a quick screencast here.