Frontier Developments explains they have ended sales of Elite Dangerous Arena, the standalone combat spinoff of Elite Dangerous, their space sim (thanks Eurogamer). They say most players are accessing Arena through the main game client anyway, and that ending the standalone version will mean they have fewer builds to support, though they also say that those who already own Arena will be able to access the game as before. Here's the explanation, which was posted a few days ago on the Frontier Forums by senior community manager Edward Lewis:

'Elite Dangerous: Arena will be removed from sale on Steam, Frontier store, and on the Xbox store. This change is planned for later today.

We’ve been looking at our metrics which suggest that the vast majority of new and regular Arena players tend to play Arena through the main Elite Dangerous client rather than the standalone Arena one. We’ve made the decision to remove the standalone version of Elite Dangerous: Arena in order to reduce the number of builds that have to be maintained and managed across Steam, Xbox One and in 2Q'17 PlayStation Network, as well as clarifying the choices for new players of Elite Dangerous on these storefronts.

Elite Dangerous: Arena continues to be available and supported as part of the wider Elite Dangerous game. Existing and new players that join the Elite Dangerous galaxy will continue to be able to enjoy the fast-paced action of Arena through the main menu. Existing Elite Dangerous: Arena client owners will still be able to enjoy Arena as they have always done.

Not much change but we just wanted to give you a quick heads up, to avoid any confusion.'