In fall 2021, the Stanford Internet Observatory offered the fourth iteration of its Online Open Source Investigation course. The class covers strategies for investigating content on social media, cryptocurrency transactions, and more. Throughout the quarter students work on an open source investigation into the topic of their choosing. We periodically published projects from the course, including an investigation called “Who Are the President of Guinea’s Facebook Trolls? The Blurry Line Between Modern Campaigning and Coordinated Inauthentic Behavior” and a two-part investigation into inauthentic editing on Wikipedia (part 1; part 2). These investigations were covered in Bloomberg and Time Magazine respectively. In this report we are publishing five student projects from the fall 2021 quarter. The projects investigate inauthentic behavior on TikTok; misinformation on Stanford’s campus; Telegram activity in Belarus; health insurance scams that run advertisements on Google; and QAnon content on Tumblr. Contact information for authors is at the bottom of each write-up.