Heroku
Heroku is a PaaS service which allows to host your apps in cloud. PaaS is something in layman terms, which lets you focus on code rather than managing the running environment (Hardware/Software) aspect of the web application. Affordable PHP hosting for masses was available from day one which is the kind of luxury Python, Java or other potential languages didn't enjoy.
PaaS address this and brings affordable and free Web Application hosting to masses. Among many PaaS providers, Heroku is one of the popular pioneer and respected member. Heroku's pricing model is generous enough to feature a free quota which is suffice to accommodate low to medium resource hungry web application. Which is a boon to hobbyist developers like me.
