Oxygen is a hosting platform by Shopify that is specifically designed for Hydrogen storefronts. It is currently available to merchants on the Plus plan but would hopefully be offered to other plans soon.
Hydrogen storefronts can be deployed to a number of Node.js/Worker platforms like Vercel, Netlify or Cloudflare Workers.
Oxygen offers a similar approach to Vercel. It enables developers to use a powerful CLI to build a Hydrogen app and push versions of the app as separate deployments. Each deployment generates a unique preview URL and details like an error log can be seen directly in the Shopify Admin.
This is a key advantage that Oxygen has over other hosting solutions like Vercel. Oxygen comes with a native integration with the Shopify Admin out of the box.