DigitalOcean feels wrong for this purpose since they provided VPS not storage per se. I would suggest hosting the website on Digital Ocean, github or something similar and hosting files on S3 or some similar service that specializes in storing files rather than providing VPSs.

The problem isn't really in the overall bandwidth usage though, it's the concurrency.

Would the $5/month droplet stand up to a surge of people coming in for a latest release, or a bit of press coverage? Would there be enough bandwidth that everyone gets the file fast or would they all slow to a crawl

What about providing a BitTorrent link? The main server could provide a backstop seed, and presumably enough other people would seed too for any decent-sized project.

P2P downloads would help cover some of the costs, but popular projects probably need a direct download link with load balancing as well.

If the project doesn't want to manage their own infrastructure, they're probably going to want a CDN or object storage provider. The most cost-friendly I've seen is OVH's RunAbove object storage, but I'd be interested to know if there is anything else comparable.

50000 downloads is ridiculously low for any popular software package. Besides, VPS are not that fast at serving static files as you think. My VPS-hosted site became like 10x as fast when I made it pull 100kb-ish javascript files from a CDN instead of off VPS harddrive.

Do users pay anything at all? Or enough to cover that trivial cost?

Oh bollocks, I thought by 1TB/month you meant in storage, not bandwidth!