Ajax
Anders Noras blogged about Ajax, "Chubby" or Smart Clients. I like the term “chubby client”. Where a “thin client” is your traditional web application with a lot of postbacks and a “thick client” is a full-blown windows application. “Chubby client” is like GMail with a lot of client-side scripting and XmlHttp posts going on. Chubby clients rock.