Linux : Databases : Mysql , Postgresql , Sybase Web : Nginx, Apache 1/2, Tomcat, Glassfish , PHP, html Management : Ansible, Cfengine Monitoring : nagios, icinga, grafana, logstash, elasticsearch Voip : Voicemaster , asterisk , ser, PortaBilling, Yate Mail : Sendmail , Postmaster , qpopper , QMAIL , vpopmail, Courier IMAP, Cyrus IMAP , Mailscanner ( Antivirus + Antispam ), spamassasin, clamav, fprot + squid proxy Various linux distributions ( Ubuntu, SuSE, Gentoo, Debian, RedHat, Centos) Firewalls (Iptables ) Routing - BGP, iproute2 (tc + ip), cisco ios scripting - perl, bash , PHP, python Virtualization - KVM, Hyper-V, Vmware ESXi , Virtuozzo, Openvz Control Panels : Cpanel, Plesk, Ensim Streaming/Transcoding : ffmpeg, RTMP Windows: Windows 2003, 2008 and 2012 Server Administration Databases - MS SQL administration Web - IIS, Tomcat, Glassfish Mail - Hmail, Smartermail scripting - Powershell Virtualization - Microsoft Hyper-V , Virtuozzo Control Panel : Plesk, Websitepanel