In the span of a few short years, Heroku has evolved from a Ruby-only platform targeting hobbyists to supporting Python, Node.js, Java, Scala, and Clojure, thus inviting developers of all stripes. What's more, Heroku provides third-party add-ons ranging from free services such as SSL and deployment audits to commercial services such as MongoHQ, Loggly, and Zencoder, to name a few. Heroku recently released a cloud database service, dubbed Heroku Postgres, that gives developers an always-on SQL database for use in applications hosted anywhere. Although the race for developer mind share among PaaS offerings is by no means over, Heroku is clearly leading at the moment.
-- Andrew Glover