Trojitá is an email program ("client") specializing in IMAP accounts (an IMAP account is one where the messages remain on a server instead of being downloaded to your local computer). It prioritizes efficiency and speed above all other goals, respecting open standards and protocols.
Trojitá also aims to be multi-platform, and functions well on everything from big desktop computers to small cellphones.
Trojitá is a stand-alone program, not part of a "personal information manager" suite. It's still in the early stages of development, but intends to remain true to its goals of efficiency, speed, and simplicity.