Sony announced that the online multiplayer feature of the PS4 will be available for free this weekend. This feature is usually only avaialble for PlayStation Plus subscribers.
Players without PlayStation Plus will be able to play online from the 20th of March at 12am PST until the 22th of March at 11:59pm. This is the perfect opportunity for PS4 players that have yet to experience the online component of their games, including the upcoming Battlefield Hardline.
This offer is only for the online multiplayer and doesn't include other features of PlayStation Plus.
Source: Playstation Blog