Open source is becoming more popular every day and offers some unique advantages compared to 'closed software' like Microsoft Windows. Some examples of what you can achieve by using Linux:

• Installing webservers by using Apache and MySQL. This combination is being used all over the world and has proven to be excellent software. Linux webservers are very stable and offer good security.
• Setting up OpenVPN connections to create secure SSL-tunnels. This can be interesting compared to commercial solutions like Cisco or other hardware boxes. OpenVPN is open source and has an excellent performance.
• Security scans by using Backtrack Linux. Linux offers the most security tools to scan your network for vulnerabilities and to perform penetration tests to see if your network really is secure.
• Setting up firewalls based on Linux.
• Database servers
• And more...

I work with all the common Linux Distributions like Red Hat, CentOS, Fedora, Suse, Ubuntu, Knoppix and some others.