This whole thing sounds phishy.
The two websites I listed are not. It's not uncommon to release for free games released commercially in the past (some of the first were Dink Smallwood and Battlecruiser 3000AD, while one of the most notable and recent one was The Ur-Quan Masters which improved the original Star Control 2 by using source code provided by the creators themselves). It has not to be confused with abandonware, where many websites just provide games not available for sale anymore without checking with the copyright holder.
Giveawayoftheday instead provides a way to advertise developer's products by offering one of them for free just for one day.