Do you mean the games are "free" but there are a lot of in-app purchases all around them?- No. There isn't any in-app payments.
So surely there are intrusive ads popping up and possibly sharing my data with third parties?- No. No ads. Not giving any info to third parties either.
This sounds almost too good to be true ...and I've learned that there's no free lunches. Where's the catch?- The games didn't bring enough revenue to pay the bills. So, I rather publish the current versions as fully free than keep them behind the paywall and let them be totally forgotten in the ocean of Android games.
So, are they fully free forever?- Don't know yet.
Where can I get these games you are talking about?Here: