Zimbra Desktop is an offline client that lets you manage various email accounts in one desktop tool. Developed by Zimbra
License: Free Personal
Zimbra Desktop is a collaboration-focused email client that integrates email, calendar, and task management, making it suitable for team environments. In contrast, Thunderbird is a highly customizable, open-source email client with extensive add-on support and a strong community, making it ideal for individual users who want flexibility.