Zimbra Desktop is an offline client that lets you manage various email accounts in one desktop tool. Developed by Zimbra
License: Free Personal
Kontact - KMail is a more integrated solution for users invested in the KDE ecosystem, offering a range of features for managing emails, contacts, and calendars. Zimbra Desktop, on the other hand, provides a more user-friendly interface with strong collaboration tools, making it suitable for both individual and business use.