For those who don't know, every 1st Tuesday of the month Playstation update the store with a selection of free games for PS Plus subscribers. There are always titles for PS4, PS3 and PS Vita. Also, because crossbuys and included it means that if a game is also available normally on more than one of these consoles then it's available free across these platforms. For example, if a game is being listed as a PS4 free game but it is also available in general on PS3 and Vita then it's also free on PS3 and Vita.
Announcements for each month's games usually happen around the last Tuesday of the month before.