Build your website or your prototype and coordinate your team.
Unless you need very specific website technology, most people can get a functional website, protoype, and access collaboration technology at very reasonable costs. The following are examples of available products.
https://www.invisionapp.com/ (better for taking existing UX/screens into prototyping)
https://www.sketch.com/ (Mac only)
https://www.flinto.com/ (Mac only)
www.asana.com (very customisable, but good templates too, boards or lists)
https://jira.atlassian.com (less user friendly for the uninitiated)
www.pivotaltracker.com (old school )
www.taskade.com (decent Slack alternative too)
www.flock.com (decent Slack alternative too)