Heroku CI vs Screwdriver: What are the differences?
Developers describe Heroku CI as "Fast, low-setup CI that’s easy to use". On every push to GitHub, Heroku CI runs your tests in a disposable Heroku app, so there’s never a wait time for a free CI worker. Tests run fast, on Performance dynos. On the other hand, Screwdriver is detailed as "Yahoo's Continuous Delivery Build System for Dynamic Infrastructure". Screwdriver is an open source build platform designed for Continuous Delivery.
Heroku CI and Screwdriver can be categorized as "Continuous Integration" tools.
Screwdriver is an open source tool with 702 GitHub stars and 107 GitHub forks. Here's a link to Screwdriver's open source repository on GitHub.