Porter can evaluate incoming events against rules you set up, and perform actions when those rules are met. For example, actions include sending an email, a web callback, or a push notification. The number of these actions that are processed each month depends on your subscription.
For example, a weather station built on Particle emits barometric pressure events every so often, and you set up a rule to have Porter notify you when the pressure drops below a certain point. Each notification sent is an action that counts towards your monthly total.