Programming or scripting in almost any language, COTS/OSS/custom architecture, implementation, migrations, configuration, administration, operations, automation, integration, testing, monitoring, and reporting. Infrastructure & middleware, application servers, database, directory, mail, www, sftp, DNS, and other networking. I generally don't do custom hardware design, network cabling, or building applications from the ground up. Superior troubleshooting and RCA. Performance tuning, optimization.