Monit is a utility for managing and monitoring processes,
files, directories, devices and network services on a Unix system.
Monit conducts automatic maintenance and repair and can execute
meaningful causal actions in error situations.

monit supports:                                        
 * Daemon mode - poll services at a specified interval
 * Group and manage groups of services, service dependencies
 * Logging - syslog or own logfile
 * Alert, start, stop and restart of services based on it's characteristics
 * MD5 and SHA1 checksums
 * Runtime Unix socket and TCP/IP port checking (tcp and udp)
 * Process status, timeout, memory and cpu usage, etc.
 * Device usage monitoring (inodes and space)
 * File monitoring (timestamp, checksum, permission, owner, etc.)
 * Directory monitoring (timestamp, permission, owner, etc.)
 * Remote network services monitoring (ping, response time, protocol, etc.)
 * System load average monitoring
 * Flexible and customizable email alert messages and notifications
 * Protocol verification such as HTTP, FTP, SMTP, POP, IMAP, NNTP, NTP, etc.
 * A HTTP interface with XML output option
 and many more features :)

WWW: http://www.tildeslash.com/monit/