(Although I would argue that Salesforce was also responsible for creating most of what we love about Heroku. That acquisition happened far earlier than people realize. They're also almost entirely responsible for its downfall.)
EDIT: Craig is right below (and he pretty much always is). When I said "created" I really meant in terms of giving them enough financial resources to keep building. SFDC exerted no influence in terms of product decisions early on (so far as I know). Re-reading my post I see that wasn't clear.