LogDog monitors messages passing through syslogd and takes actions based on key words and phrases (which can be regular expressions). It has a configuration file which allows you to specify a list of key words or phrases to alert on and a list of commands that can be run when those words are encountered.
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.
SendSNPP is a program for sending messages through an RFC1861-compliant SNPP server. SNPP stands for Simple Network Paging Protocol, and is used by a wide range of paging and cellphone providers for sending pages and text messages. SendSNPP requires no special modules, and has been tested on Linux and Windows systems. It has a straight-forward interface, making it very easy to use.
Alert Manager allows you to monitor the output (exit status or text) of any system command and take action when a command fails or succeeds. It was created to handle all alert commands (emailing, paging, etc.) for a production environment in which it is not permissible to lose a single message. It has a very flexible configuration file that allows the creation of "alert chains", chains of alerts, each with its own alert command, fallback command, success command, and other options. It has a method for passing messages (alert text) from the commandline to the various alert commands defined in the configuration file.