Yugma: Online Collaboration Tool

https://www.yugma.com/ Free, unless you want more robust usage features. " Yugma is the easy, secure and reliable collaboration tool for Windows, Mac and Linux. With Yugma, you really can collaborate better. Yugma enables any group to spontaneously collaborate on projects in real-time. Collaborate anytime with off-site team members, give virtual presentations, host webinars, streamline workflow, provide remote tech support, and much more."