Okay, so it’s not technically Destiny, but it’s inspired by Destiny, and it’s not like the regular version of Destiny is even out on PC, anyway, so this is what you’ve got. And it’s free.
It’s called Project Tiger, and it was made by Destiny fan Brenton Whitwell.
“So a while ago some artwork was posted around here of Destiny imagined as a Low-Res 2D side-scroller, and really got my [sic] inspired to make a playable proof of concept of it, and so… well I made one,” he explains on Reddit. “I made this over the past few months in some spare time and had a lot of fun with it, and I thought it would be a great way to help celebrate Bungie Day!”
It’s mostly just running from one place to the next and shooting stuff, and there’s no real story. So, basically, it’s exactly like Destiny.