(Another ex Heroku person here) At the time of acquisiton (Dec 2010) the Bamboo stack was the only GA stack, Cedar was in beta which used buildpacks internally

(Another ex Heroku person here) At the time of acquisiton (Dec 2010) the Bamboo stack was the only GA stack, Cedar was in beta which used buildpacks internally but custom buildpacks didn't come to 2012 https://blog.heroku.com/buildpacks https://blog.heroku.com/buildpacks