Join Date:Joined: Mar 2009
You may be referring to Aptoide which is sort of an aggregator of multiple user managed stores. These users may or may not provide apps that you usually have to pay for in Google Play. Its like torrents, the medium is not illegal but the content may be.
Of course downloading such apps from unofficial sources without paying for them is illegal and I do not recommend doing this at all because you are directly hurting the developers who spend a lot of time and resources to make apps and games. It is as bad as stealing. Also, there is no guarantee that any app downloaded from any store on Aptoide has not been tampered with and may contain malicious content like trojans, etc. You download apps from unverified sources at your own risk.
I must emphasize again, it is morally and legally wrong to commit the act of piracy and apps do not cost much at all, if you can afford a smart phone you can surely spend a couple of bucks now and then to buy apps else find what you need in the free app universe.
Might I suggest GetJar as an alternate which provides some paid apps for free somtimes or other unlocks, etc.