Amazon Launchpad is described as 'Launch platform for cutting-edge, new products' and is an website in the Online Services category. There are more than 10 alternatives to Amazon Launchpad, not only websites but also apps for a variety of platforms, including Mac, Windows, Linux and Android. The best alternative is AlternativeTo, which is free. Other great sites and apps similar to Amazon Launchpad are Product Hunt (Free), alternative.me (Free), Top Best Alternatives (Free) and MoreGamesLike.com (Free).
AlternativeTo let you find new Windows, Mac, Linux, online and mobile software based on applications you already know instead of useless categories. AlternativeTo is a new approach to finding good software.
When I am exploring alternatives to a product or service, I often to go Google, type "[product] vs ", and just see what it autocompletes. That usually tells me the most popular competitors. If I want to be thorough I'll do the same for the competitors, etc.