I have been working on open source tools from past 5 years. I have a good knowledge on some of the below mentioned tools:
1. Open Source web proxy with content filter
2. Open Source Load Balancer
3. Linux HA Cluster
4. LAMP
5. Open Source Virtualisation
6. DNS,DHCP services on linux
Windows Administration Skills:
1. Active Directory
2. IIS
3. Exchange Server 2013 Administration
4. Windows Application Cluster
VMWARE ESX 5.5 Server Administration