With any project, it's nice to just get everyone in the same room once in a while. That, however, can be a problem when people are in different locations, across town or on different continents.
These free and paid solutions can help keep everyone on the same page.
Skype can handle up to 25 people on a conference call. It's free for participants that have Skype. For people who aren't on Skype, you can include them on their mobile or landline number for a small fee.
A great option if you want to try group collaboration. Many already have Skype installed on their computer or smart phone.
Edmodo is a free and easy way for teachers to connect and collaborate with students, parents, and each other. It is tightly integrated with Google's G Suite for Education and Microsoft's OneNote & Office. You do not need to remember multiple passwords, or click out of Edmodo to access your Google Drive or to collaborate using Google Docs.
Supports both desktop PC's and mobile apps.
Google's G Suite for Education includes an on-line conferencing function with Hangouts Meet. Hangouts can handle up to 25 people and the screen automatically focuses on whoever is speaking and intelligent muting prevents background noise.
For large group training and conferencing try WebEx or GoToMeeting.
A presenter can deliver an audio lecture, supplemented with PowerPoint slides for real time annotation. Attendees can chat among themselves via text or audio while the presentation is occurring and submit questions to the presenter.
While not free like some of the other solutions, both allow you "try before you buy".
Looking for low/no cost option for sharing presentations, talks and meetings?
Create a PodCast or MP3 file of the event.
While not "real time", you can create these files using free software that your collaborators can download and listen to on their schedule.