What are the best alternatives to Heroku?

I recently started using DigitalOcean's new app platform. It's new and still has some kinks, but they've integrated all of Heroku's open source build packs, so migrated from Heroku (if that's what you're doing) is pretty painless.

https://digitalocean.com/products/app-platform/

https://render.com is one

I am writing an open-source Heroku-like PaaS on top of AWS out of pure Terraform.

I wanted the high-level abstractions of a PaaS like Heroku, but I didn't want to pay a premium. I also wanted to maintain everything in a declarative Terraform config and have the opportunity to make low-level additions when necessary.

I've used it in production for more than a year at my company for running distributed crawling and machine learning jobs.

https://provose.com

https://www.hatchbox.io/ is a good option for Rails projects.