StartupBase is described as 'community of makers and early adopters to share & discuss the latest products and ideas. It is a place to discover and get early access to exciting new startups'. There are more than 25 alternatives to StartupBase for a variety of platforms, including Online / Web-based, SaaS, Android, Mac and Windows. The best alternative is AlternativeTo, which is free. Other great apps like StartupBase are Product Hunt (Free), alternative.me (Free), Top Best Alternatives (Free) and switching.software (Free, Open Source).
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.