Heroku is a cloud platform that supports various programming languages like Ruby, Node.js$,$ Python, Java, PHP$,$ and Go$.$ It simplifies application deployment and scaling. It provides developers with tools and services to streamline application development, automate infrastructure management, and facilitate the deployment and scaling of applications without worrying about the underlying hardware or infrastructure setup. It does so by abstracting many underlying infrastructure details. Companies like Heroku would be considered as:

a$.$ Software as a Service $($SaaS$)$

b$.$ Infrastructure as a Service $($laaS$)$

c$.$ Neither of these options

d$.$ All of these options

e$.$ Platform as a Service $($PaaS$)$