Two big tech companies that want to define the future of gaming—Microsoft and Amazon—are showing more of their cards. Both companies want to use their eye-watering investments in cloud computing to stream games over the internet so that people can play them on any kind of hardware, including devices that are normally too wimpy to support the most graphically-demanding games, such as inexpensive set-top boxes. 

But their efforts aren’t created equal. On Monday, Amazon said it will begin letting any Amazon Prime member play its game streaming service, Luna, for a seven-day trial starting June 21, when its Prime Day shopping event starts. After that, the service will cost $5.99 a month for a pretty meager selection of games or $14.99 for a better selection of games made by the publisher Ubisoft.