We use DigitalOcean mainly to provide remote development environments for Zulip contributors in situations where developing locally using our Vagrant setup isn't practical. There's a range of reasons:

• Situations where one needs a public IP address and SSL certificate (e.g. Facebook's OAuth system require that even for testing)
• Giving a contributor a development environment when their computer doesn't have the few GB of free RAM needed to run one locally
• Developer sprints, where our snapshot-based system can provision a working development environment for a potential new contributor in under a minute. This use case is particularly great because a machine that one only needs for 3 days is essentially free with Digital Ocean's pricing.
• A backup development environment when someone's laptop is being repaired.

One could do all of this with many hosting providers, but we've found it particularly convenient to use Digital Ocean for these applications.