Platforms: Linux (Gentoo, Debian, CentOS, Fedora Core, Red
Hat, Ubuntu), UNIX (FreeBSD, Solaris), CiscoIOS, Cisco,
Linksys, D-Link, 3com.
Languages: C/C++, Perl, Shell, SQL, HTML.
Databases: PostgreSQL, MySQL, etc.
Firewalls: iptables, pf, ipfw, etc.
WEB-servers: Apache(1/2), Nginx, Lighttpd, etc.
FTP-servers: ProFTPd, vsFTPd, etc.
Mail-servers: Sendmail, Exim, Postfix, Cyrus, Dovecot, etc.
DNS-server: Bind.
VPN: OpenVPN, IPSec, PPTP, L2Tp, Vtund, etc.
Proxy: Squid, socks5.
Security: Syslog, Snort, etc.
Monitoring: Nagios, Cacti.
Version Control: CVS, SVN, Git, Perforce etc.
Bug Tracking: Bugzilla.
Backup: Amanda.
VoIP: Asterisk/Callweaver/FreePBX, SIP, H.323, IAX, PRI (Call centers/Office PBX).
Other: Anti-DDOS, Anti-SPAM sollutions.