I use ifttt + pushbullet for these kinds of tasks.

Pushbullet also has an api so you can directly push notifications to your device(s).

I wouldn't mind a clone of ifttt that let me customize my own channels.

The problem with these notification tools is that if something isn't already defined for you you're kind of sol. You can sort of hack it by making the thing-you-don't-have-a-channel-for output to a channel that is supported. E.g., if you want to be notified when your local library has a book in stock, you can get your library to email you, and then filter that in gmail, and have ifttt trigger on that email to pushbullet.

Kind of a hassle. #firstworldproblems