Recode has done an excellent job summarizing and linking to ways you can watch the debate online.
CBSNews,com (CBSN available on Roku, Apple TV, smartphones and other devices)
Watch the debate in virtual reality (requires compatible headset and app)
How to join: For the full VR experience, visitors can use the AltspaceVR app on the Oculus Rift, HTC Vive or Samsung Gear VR. For the 2-D experience, users can join using a PC or Mac. Join NBC’s Al Roker in virtual reality (no headset required)
From the Commission on Presidential Debates:
Facebook, the exclusive social media sponsor for the first and third presidential debates, will be on site at the debate host universities. Members of the media, students, and the campus community will be using Facebook Live to broadcast and show what is happening at the debate site. People on Facebook in the U.S. and around the world will be able to watch these videos live, ask questions and comment with their reactions. Facebook will also have an interactive touch screen to show the conversation on Facebook about the candidates and the issues. (facebook.com)
Snapchat will be covering each debate on-site via a “Live Story.” These Live Stories will allow users on Snapchat to experience the debates from the many different perspectives of students from the debate host universities, volunteers, media and many others. These compilations of Snaps are designed to encourage the conversation long after each debate is over. (snapchat.com)
Viewers will also be able to watch live streams of the debates. Some of the websites and platforms that will feature debate live streams are: ABC News, Buzzfeed News, CBS News, CNN, C-SPAN, The Daily Caller, Facebook, Fox News, Hulu, Huffington Post, NBC, PBS, Politico, Telemundo, The Wall Street Journal, Twitter, Univision, Yahoo, YouTube.