xmailheaders is a mail notification utility that is based on the "mailbox" utility that's avilable on Solaris workstations. The idea is that it sits on your desktop somewhere, periodically polling the mail server/spool for new messages. New message headers are displayed as they come in. Supported mailbox formats are POP3, IMAPv4, and Unix mbox. SSL-based password authentication is also supported for POP and IMAP.
xstress is a small yet powerful tool to stress test SMTP mail servers. xstress creates multiple threads and sends mail messages with varying subjects, "to" addresses, and body texts. Mail attachments are supported. All the parameters are highly configurable. For example, you can configure the number of threads xstress creates, SMTP timeout, attachment files, "to" address, "from" address, etc.
xtalfind checks whether any XTAL is suitable for a HAM radio circuit (TX, RX). Given a base XTAL frequency, it shows you all possible uses within HAM bands. It features CW TX and direct conversion RX. It supports 455kHz, 10.7MHz, and custom IF value receivers, DRM, and SDRadio applications.
xtell allows you to send messages between computers running xtell server. It is easy to use in scripts (i.e. to notify you when you get a mail or something else happens) or as a network-aware replacement for write(1). It was originally based on Michael Bacarella's ident2 server and Jozef Knepp's VMS implementation.