Please find below a selection of useful tools.
Linux Malware Detect (LMD) is a malware scanner for Linux released under the GNU GPLv2 license, that is designed around the threats faced in shared hosted environments.
Chkrootkit is a tool to locally check for signs of a rootkit. A rootkit is a set of software tools that enable an unauthorised user to gain control of a computer system without being detected.
Lynis is an open source security auditing tool. Used by system administrators, security professionals, and auditors, to evaluate the security defenses of their Linux and UNIX-based systems.
The Phoronix Test Suite is a very comprehensive testing and benchmarking platform available for Linux, Solaris, OS X, and BSD operating systems. The Phoronix Test Suite allows for carrying out tests in a fully automated manner from test installation to execution and reporting.
Munin the monitoring tool surveys all your computers and remembers what it saw. It presents all the information in graphs through a web interface.
Apache SpamAssassin is a leading Open Source anti-spam platform giving system administrators a filter to classify email and block spam (unsolicited bulk email).
Fwbackups is a feature-rich user backup program that allows you to backup your documents anytime, anywhere. Fwbackups can backup files to locally attached media like USB memory keys or to a remote computer such as a backup server, making it perfect for both home and corporate environments.