System requirements: A user API key (which one can request from the
website at <http://www.pushbullet.com>), and one or more
devices to push messages to which may be any one of an (Android
or iOS) phone, a (Chrome or Firefox, or Opera or Safari)
browser or the (Windows or Mac) desktop application provided
the corresponding Pushbullet 'app' has been installed on any
one of these.