Geary is a simple and lightweight email client that supports email threading (some call it conversation mode). It is still in the early development stage, but it does show plenty of potential to become a great email client. Being a simple and lightweight app, Geary has trimmed most, if not all, of the fat found in many other email clients. It is pretty simple in interface and features, and yes, it is also lacking some important functions like integrating with address book and connect to multiple email accounts.