SendEmail is a lightweight, completely command line-based SMTP email delivery program. If you have the need to send email from a command prompt this tool is perfect. It was designed to be used in bash scripts, Perl programs, and Web sites, but it is also quite useful in many other contexts. It is written in Perl, and is unique in that it requires no special modules, and supports any platform that runs Perl. It has a straightforward interface, making it very easy to use.
Chandler is a standards-based "Note-to-Self Organizer" designed for personal and small-group task management and calendaring. It consists of a desktop application and Chandler Hub, a free sharing service and Web application. You can also download and run your own Chandler Server.
XCmail is a MIME and multi POP3 capable mailtool for X11 using the Xclasses X11 layout library. Its main purpose is to read and write mail, allowing any kind of data to be attached. It can handle MIME types, has helpers to show different types, and can encode and decode binary data into ASCII to allow it to be transported as mail over the Internet. It has many built-in functions such as 2 vCards, unlimited POP3 servers, SMTP, SMTP after POP3, SMTP-AUTH (RFC2554), addressbook, encoders, filters, a special spam filter, spell checker, xface, and a new "virtual folder" concept. It also uses external programs to enhance its feature set. XCmail can be extended through a plugin interface.
IlohaMail is a lightweight, multilingual Webmail client that is easy to use and install. It runs on a stock build of PHP, and does not require databases (although database support is available) or the IMAP library (it is powered by a custom IMAP/POP3 library). It also includes basic PIM-like features, including a calendar/scheduler, a full fledged contacts manager, and a bookmarks manager.
MIMP is a version of the popular webmail client IMP intended for mobile phones and PDAs. Basic webmail functionality is implemented, including mailbox viewing and paging, viewing messages, deleting, replying, forwarding, and composing new messages. It utilizes the Horde Application Framework.
i.Scribe is a cross platform email client, address book, and calendar. It is small, fast, and easy to install. It has multi-language support, and currently includes English, French, Chinese Traditional,Italian, Portuguese, Brazilian Portuguese, Japanese, Vietnamese, Czech, Polish, Spanish, German, Russian, and Dutch translations. It is very expandable via a plugin interface, and uses its own HTML engine (and not IE when run on Windows). It supports POP3, [E]SMTP, MIME, IMAP4, and MAPI. An integrated contact database and calendar are included.