Instant messaging on a tape delay
What it is and when you'd use it
laterti.me is a site for recording comments along a timeline. Comments appear in real time as they're made, at the point on the timeline they apply to. As you play the timeline in normal time (eg. as you watch a corresponding video), relevant comments only come up when they're relevant.
Say you're watching an episode of a TV show you've recorded, which a friend of yours has also recorded, but hasn't watched yet. You want to riff about your thoughts while you watch it, but you don't want to spoil the episode for your friend. You can go to laterti.me and create a new timestream for you and your friend to watch the episode on; if your friend decides to watch it later (or even while you're half-way through), you'll see their reactions, to the video and to what you're saying, as they write them.
laterti.me is also pretty awesome even if you're just watching the video at the same time, since it lets anybody watching pause for a break, or rewatch a line they didn't quite catch, without making everybody else wait up.