The short answer is all of them. Windows, Mac, PlayStation, Xbox, Linux, Android, iOS and Amazon.
What’s the long answer? Build your creation with tools that will place your game on the most platforms. It’s not as hard as you would think. I haven’t dug too deep but I’m a little sad that “No Man’s Sky” is intintially just on PlayStation 4 and Microsoft Windows. I can only assume it’s because of the way they coded it.
Most coders are like musicians. Find a brand of instrument that works for you and stick with it. If you start off cheap, use what you got to make money and then use that money to buy better equipment.
On second thought indie gamers are NOT like musicians. Most coding tools are FREE! To be a Xbox or PlayStation Dev is FREE! Yes it costs to put your games on iOS, Android and Steam but it really evens out once your quality product picks up steam, haha.
So, the first step to making your game is choosing a tool or program that is universal:
For Windows, Mac and mobile games try www.coronalabs.com Corona SDK. It is now free and very flexible.
For everything try either www.unity3d.com or www.epicgames.com. These engines are both free to use but you might have to pay royalties if your game makes a huge profit.
In the end there are many ways to make your game available for others to play. The main thing is to make it. Don’t wait too long thinking about it. Gamers can’t wait to play something new. Give it to them sooner than later and fix the bugs as you go along.