Digital Ocean is a traditional VPS provider who recently added a product that competes with AWS S3 and a product that is docker hosting as a service, which I hope is a valid alternative to EC2 autoscaling. They have a thing with gitlab to run your continuous integration pipeline. They have a few more things.
Heroku is a platform as a service. They provide an alternative to EC2 autoscaling. Also available is postgre, Kafka, redis, MongoDB, MySQL, and a few other things I rudely assumed aren't important enough to mention as a service.
Vultr and linode also offer block storage in addition to traditional VPSs.
Ovh has something called object storage.
Auth0 is willing to be your "user authentication as a service" which also includes something like AWS lambda.
Spotinst will help you get cheap "spot instances" for AWS/GCP/Azure. They also have an AWS lambda competitor and an object storage (I think this one is literally a JSON object storage for your FaaS, not actual files). Not much of a primary service provider.
I consider AWS, GCP, and Azure to be megacorporate monopolies and would prefer to support an underdog. But I'm not aware of any 4rth competitor that comes close to what those 3 actually are. The ones I mentioned probably average at 10% and maybe DO or heroku peaks at 40%.
I would love to hear more about cloud providers who are becoming more than just VPSs to take on AWS.