Last summer belonged to Rocket League: Psyonix's smash hit car football game that released on PS4 and PC in July. For one month after launch, PlayStation Plus subscribers could download the game free of charge, proving a huge factor in the game's success.

In its first month, the game was downloaded more than two million times, both for free on PS4 and for sale on PC. The game has endured beyond its freebie status however, now topping the five million units sold – not including the copies downloaded for free.

It's a figure also matched when it comes to DLC sales. To date, the game has generated $110 million (£76m) for Psyonix, according to Forbes. The business publication was told of the figures during an interview with Psyonix vice president Jeremy Dunham. The VP also revealed that there were five million active players during April 2016 - aided by the release of the game on Xbox One in February.

The game's post-launch support has helped it endure. Free updates have introduced new maps and modes, while paid DLC added new vehicles and items – some based on licenses like Back To The Future, Batman v Superman and The Witcher.

The secret to its success, according to Dunham, is treating it like a free-to-play title. "It makes sense that you keep developing and developing because it's a live project. In our case, we came out with a premium price but we keep supporting the game as if it's a like a live product. And that's working for us because of the DLC we do, that sort of creates the need to make DLC that's more than just 'Oh here you can put a special item on your car.' We're actually trying to add substantially new gameplay."

Over the winter months Rocket League included a mode based on ice hockey, and in late April released Hoops, a new Basketball-like mode.

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