getmail is intended as a simple, secure, and reliable replacement for fetchmail. It retrieves email (either all messages, or only unread messages) from one or more POP3, SPDS, or IMAP4 servers (with or without SSL) for one or more email accounts, and reliably delivers into qmail-style Maildirs, mboxrd files, or through external MDAs (command deliveries) specified on a per-account basis. getmail also has excellent support for domain (multidrop) mailboxes, including delivering messages to different users or destinations based on the envelope recipient address.
mpop is a small, fast, and portable POP3 client. Its features include header-based email filtering (filter junk mail before downloading it), delivery to mbox files, maildir folders, or a mail delivery agent, a very fast POP3 implementation, many authentication methods, and good support for TLS/SSL.
Roundup is an issue-tracking system that is simple to use and simple to install. It has command-line, Web, and email interfaces. It manages a number of issues (with flexible properties such as "description", "priority", and so on) and provides the ability to submit new issues, find and edit existing issues, and discuss issues with other participants. The system facilitates communication among the participants by managing discussions and notifying interested parties when issues are edited.
Hotwayd is a POP3/SMTP to HTTPMail (WebDAV) gateway. HTTPMail is a somewhat undocumented WebDAV-based protocol used by a variety of mail servers including Hotmail, MSN, Lycos, and Spray. Hotwayd allows you to use any standard POP3/SMTP mail reader to send and receive mail via these servers, similar to the way that Outlook Express can access a hotmail account. It supports features such as folder selection to get folders other than the inbox and proxy server support (if you require a proxy to access the internet).
Collaba is a multimedia collaboration and communication server built to provide digital workspaces to virtual educational, corporate, and other communities. It features secure email (Web, POP3/SMTP, crypto, and anti-spam), online forums (Web, RSS, NNTP, and podcast), blogs (Web, RSS, podcast), multimedia chat (text, multimedia panel, etc.), personal and group calendering, address books, bookmarks, an online Web page editor, file services and CMS (Web, WebDAV, FTP, SMB, CIFS, anvi-virus API, and ClamAV support), digital portfolio, dynamic news board, directory access, support for multiple independent communities on one server, Single-Sign-On features (built-in support for LDAP, CAS 2.0, JAAS, SMTP-Auth and more, powerful developer API), full online server management, anti-spam (RBL and filters), anti-virus support, centralized management with LDAP directories, Web publishing of personal, group or general web sites, developer APIs, and much more.
Mahogany is a GUI email client for the X11/Unix, Windows, and Mac platforms. It supports a wide range of Internet protocols (IMAP4, POP3, ESMTP, NNTP) and encrypted communications using SSL, includes full MIME support, and aims to be fully standard-compliant. It allows the use of unlimited number of servers, supports filters and identities, and offers optional HTML viewing and much more.
KONSEC Kolab Server is a highly scalable, cluster-capable messaging and collaboration server that is based on the outstanding open source project, Kroupware. The KONSEC Konnektor is a simple client extension that gives Outlook complete group functionality through the Kolab Server, which employs the open standard IMAP together with ACLs, thus enabling you to collaborate in a unique mixed Windows/Linux environment.