Dropboxcan be as used a common filing cabinet through which instructors can provide documents, such as homework assignments and handouts, and media files for the entire class. Using Dropbox as a homework drop has the added benefit of providing a time-stamp for the submissions. Students can share Dropbox folders with each other and so collaborate on joint assignments.
Piazza is a question-and-answer system designed to streamline class discussion outside of the classroom. It could be used as students' first recourse for seeking answers to their questions about the course, lecture or reading material, or the assignments.
Instructors may use Piazza for dissemination of materials (e.g., homework and lecture slides) and online class discussions. Piazza is a venue to ask questions, discuss problems, and help each other out. If instructors would like to include "participation" as parts of the final grade, Piazza may be a helpful tool to record students' participation for the course. Instructors may also use Piazza for all course announcements.
Many students will want to share their videos with other students, but not necessarily make them public to the whole world on the internet. In this case you may find it useful to make your video "unlisted". This means that only people with the link can view the video, so no one would be able to search and find it by accident.
To do this, upload a video to YouTube then in that video's settings, change the privacy from public to unlisted.