Joe Danger was the first commercial game release from No Man's Sky developer Hello Games, and as part of keeping it alive they've put it up online free to play in your browser.
You get to play with Joe Danger Touch and Infinity with "improved visuals, on Mac/PC/Chrome/Linux, dynamic resolution, mouse and keyboard support" according to the Twitter announcement.
Last year they revived the classic for the Apple App Store after noting an email they received from the mother of a child with Autism about it who loved it, and so now they're doing the same for PC players and in an expanded tweet they said: "It's sad that many games slowly die, and we've been trying to think of a way to let Joe live on forever, and reach the most people possible. This is hopefully one way of doing that. We owe this and more to him.".
You can play it online here.
Another way developers can keep old games alive is by open sourcing them, especially if they no longer plan to sell them, or even if they do want to continue selling them they can just open up the game code. Hopefully over time more will do that.