Zapier connects the apps you use. Say you want your email app to talk to your dropbox, Your twitter to work with your slack, your alarms to work with your Trello- That is where Zapier comes in oh so handy!
As long as the apps are Zapier compatible- they can be integrated to work together. We have found this great for making the clients needs easier to accomplish.
400+ App Integrations
Top Zaps for Evernote
Top Zaps for Facebook