Domains: ActiveDirectory, OpenDirectory, NIS, LDAP
WebServers: IIS, Apache, Tomcat, Nginx, lighttpd
Networking: VPN, IPSec, PPP, SSL, SSH, Telnet, TCP/IP, UDP, BGP, SNMP, SMTP, IMAP, POP, FTP, SFTP, SMB
Virtualization: VMWare ESX, Hyper-V, VirtualBox, Parallels, specific to UNIX things like LPAR/VPAR, Zones, WPARs, Docker, chroot.