If you don't already know BlackMart Alpha, then here's a quick primer (you could also read other posts on NL about it)

What is BlackMart Alpha
It is an alternative app store to Google Play Store, but here the paid apps are free. I use it, and I've had success with it. It has its downside though (more of that in a bit)

How does it work?
BlackMart Alpha works on the principle of 'crowdsharing' (call it file sharing if you please, I no sabi English), I upload any app to BlackMart server, and someone else that has BlackMart Alpha installed can also download it for free (whether I paid for it or not, doesn't matter).
I've done both a blog post, and a YouTube video if you want more clarification
BlogPost >> http://echo.com.ng/2013/howto-get-paid-apps-for-free-ios-and-android/‎
YouTube vid >>
https://www.youtube.com/watch?v=xgHafGNUMCc

Pros
Obviously, you can get paid apps for free with BMA
You could also download the apk of any app and later send to others from your file manager (if you just plan to download a file and not install it). Unlike Google Play Store that forces you download and install her apps. There are ways of also sharing your downloaded apps anyway, with or without Flash Share/All Share Play etc. Not the focus of this guide

Cons
You have to enable "Install from unknown sources" in your Application (or Security) Settings, and too bad many peeps don't like it
Since whatever you're downloading was previously uploaded by another BMA user, it could be used by malicious coders to distribute malware apks, so your security while you use this app is totally up to you

Endpoint
Ask questions, get answers.