What tools a freelancer uses is a great indicator that they have processes in place and are focused on an effective and efficient workflow. Just as the best developers use the same tools, the best marketers use the same tools, etc. An experienced freelancer should know what tools will help them get the job done best.

A freelancer's stack should include: Slack, Asana, Trello, Harvest, Google Office Suite; for marketing related - Buffer, Hootsuite, Google Analytics. If you're looking for someone with some tech or dev experience, they should know Github and Bugspot, for example.