What are the top 3 pre-launch campaigns that you saw?

I found the Robinhood app and the Harry's razors. I'm looking for more, preferably on software projects.
Mars NegretteFounder, LOLA. Assistant for relax. · Asked
3
Slack

Be less busy. Real-time messaging, archiving & search.

During the preview release, 8000 people signed up for an invite to try Slack. Two weeks later, it was 15k. Sure, there was a press blitz thanks to the team members but I think it's pretty darned impressive. Source: http://firstround.com/review/Fro...
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