Leo's pick on episode 373 of MacBreak Weekly is a free iPhone email app that now goes by the name of "Hop". It originally launched as "Ping", but had to change its name after a dispute with the maker of Ping golf clubs.
Hop turns traditional email into a real-time chat conversation. It also makes it easier to include media and documents in email messages. The idea of Hop is to eliminate the need to use multiple methods of communication, consolidating everything into email.
For more on the Hop app, check out episode 373 of MacBreak Weekly.