Protocols: HTTP, SMTP, FTP, SSH, SCP, RSYNC<p>Formats: HTML, XML, JSON, CSV, YAML<p>Languages: SQL, JS, a backend language like Python<p>Version control: Git, Mercurial<p>The *nix command line and it's tools: grep etc.<p>An extensible editor (you only need one) and it's plugins: Vim, Emacs, Sublime, etc.<p>Social skills: working well with others, working for others, others working for you (aka leadership), conflict resolution, etc.