Sony appears to have added the option to rent games through the PlayStation Store. As spotted by MP1st and PSN Stores, the interface suggests you can select to rent a game for 1 day, 7 days, or 30 days. As for the "free" pricing, that's probably just a placeholder until the service actually goes live.
It's quite likely this could be in preparation for the PlayStation Now streaming service set to roll out in North America later this year. On NeoGAF, a user allegedly found the following notification from SEN's account management, services list, after purchasing the 30-day trial.
Earlier this week, Gaikai concept art suggested that rentals for PS3 games could cost anywhere from $4.99 to $5.99, though there was no rental length associated.
PlayStation Now was first revealed at Sony's CES 2014 keynote. The new service will allow gamers to stream PS1, PS2 and PS3 games to numerous devices, including the PS4, Vita and other Sony-branded devices as well. A closed beta for the service began at the end of January, but the full service is expected to roll out this summer.
In addition to single game rentals, PlayStation Now will also have a subscription option similar to Netflix. Pricing for the monthly subscription has not yet been announced.