Blackmart Alpha is described as 'market alternative to the Google Play Store for tablets and smartphones with Android operating system, from Blackmart you can download many applications'. There are more than 25 alternatives to Blackmart Alpha for a variety of platforms, including Online / Web-based, Android, Android Tablet, Windows and Kindle Fire. The best alternative is F-Droid, which is both free and Open Source. Other great apps like Blackmart Alpha are Aptoide (Free), APKPure (Free), APKMirror (Free) and Fossdroid (Free, Open Source).
Aptoide is a distributed marketplace for mobile applications which runs on the Android operating system. In Aptoide, unlike the default Google Play Store, there is not a unique and centralized store but each user manages their own store.
In an effort to make things easy, and maybe even fun, AndroidPolice.com created APK Mirror. Over the past several months, they've been working to build a smooth, reliable, trust-worthy site to host the downloads users love. You also can upload APKs to the site yourself.
The project's aim is to promote free and open source software on the Android platform. Fossdroid takes its data from F-Droid, but organizes apps in an attractive, Google Play-like arrangement with the ability to view apps by popularity.