I think even Heroku is not the first company offering this to public. There was an app called Teatro.io which did the same in 2014. It's down now, but I've found https://web.archive.org/web/20140614011544/http://teatro.io/.

I remember using ephemeral Heroku deploys in the dev pipeline well before I knew Netlify was a thing. That was pretty much the last major innovation I saw from Heroku, before Salesforce decided they'd grown fat enough to milk.

But...there were also pipelines. A deploy preview is essentially a staging or pre-prod environment. Or going from draft to published.

There was a company called Runnable that had a product offering, but if I recall correctly was acquired by MuleSoft and shut down.

Their first round was in 2012, and even though I believe they had a different product originally, their preview environment offering predated Heroku’s.

They were in fairly wide "unofficial" customer usage for a year before that too I think.

source: my last day at Heroku was a year prior to that post, and I recall using them.