Watchout
I simply wanted to watch videos in sync with my long-distance girlfriend; but all the existing options sucked, so I decided to build one myself. My focus was on user experience, which led to the lack of sign up / login screens and latencies in synchronized playback.
Watch out for the videos, together!
Watch any youtube and vimeo videos together. No sign up needed. Unlimited number of viewers. Enjoy perfect synchronization freely and anonymously.
Of all my passion projects, this one took the least development effort and shortest time to launch. However, it was clearly the most successful, reaching 1k MAU by the end of the month. It's also the only project I decided to launch on product hunt.
More details to come.