Sega has begun releasing mobile versions of classic titles from its vast catalogue of games with the arrival of the first five games in its Sega Forever service.

The first games available, on both Android and iOS, are Sonic the Hedgehog, Comix Zone, Phantasy Star II, Kid Chameleon, and Altered Beast. And Sega plans to release additional titles every two weeks.

The games can be played offline but people can save their progress online if they wish to do so. Sega says it hopes to eventually add multiplayer options to many of the games in the collection.

The games, as with a lot of gaming apps, are free with ads. However, these ads do not annoy players or hinder the experience by interrupting gameplay. Players will have to pay $1.99 in the US and £1.99 in the UK to turn off the ads.

“The games were never designed for ads or in-app purchases, which is why weve maintained this faithful emulation experience,” said Mike Evans, Sega Network CMO, speaking to GameIndustry.biz. “Weve spent a lot of time looking at the analytics from the soft launch in the Philippines to understand how we can get this model to be the best for the game experience itself whilst balancing the commercial needs we have.”