The basic system with which we are working - a Debian / Ubuntu (optional, but very rarely OpenSUSE, CentOS).
Working life: Apache, Nginx, PHP, MySQL, FTP (vsftpd), Mail-server (Dovecot + Postfix + Web interface Roundcube mail), SVN, Asterisk (VoIP), SMS-Server for GoIPx-Gateways, Samba (work with shared folders on the network), Distribution of Internet traffic in a local area network (Internet gateway), Squid/Dansguardian for content filtering in the workplace, VPN/OpenVPN to access internal company resources from outside. Setting up and working with SIM-Bank Elgato and GSM-gateways Elgato and GSM-gateways GoIPx.
Remote access to a computer problem and the solution of the problems with the operation of the software. The main condition - that the computer had a hook up to the Internet.
Tips and tricks for working with the software configuration, the solution of the problems.