A project management tool of some kind is necessary with outsourced workers in order to keep all resources, task lists and progress centralized. Here are a few of the tops one to consider:

Basecamp -> The classic team task/project management tool.

Asana -> A simple new comer to the space that's definitely turning heads and helping teams execute.

Flow -> A great way to keep everyone on the same page and you're project moving forward.

Google Drive -> Kinda of a hybrid cross between Dropbox and a basic project management tool, Google Drive basically pulls in all the Google Docs tools and keeps everything up-to-date in the cloud. The collaborative aspect comes in when multiple people view the same document.