UNIX, FreeBSD 4...10, Linux(Debian/Ubuntu/RHEL/Fedora/CentOS), Networking(TCP/IP, VPN), DNS, bind, apache, nginx. Have some skills of electronics.
Squid, squidguard, socks.
VPN: openvpn, mpd(freebsd), IPSEC/L2TP(openswan, racoon), PPTP, PPPoE
Asterisk, AsterCRM, FreePBX.
Microsoft CRM 2011, ADFS.
Alfresco
OpenStack