I think overall Coolify is a bit more modern. It uses some different components (e. g. Traefik vs Nginx for reverse proxying), and includes a UI in its basic package (Dokku was CLI only for a long time, now they have Dokku Pro with a Web UI). Otherwise it looks like the architecture is pretty much the same.
Re: business model: both Coolify and Dokku are open source, so even if their development stops, you can continue to use them no matter what. (You do have to pay for your own servers though :-) So it's not a PaaS in the traditional sense (like Fly.io or Heroku), but more like “build your own PaaS” thing.
We'll also soon support nginx via docker labels, which will work around issues where Docker sometimes assigns random IP addresses (and unlock TCP/UDP proxying as well).
I can't say anything else about Coolify since I haven't used it in a while, but I'd be curious as to what other parts are more modern about Coolify than Dokku.
Wow, looks like Dokku got a lot of upgrades since last time I used it thoroughly. I'm wondering though, why support four different proxies?
About the modern part: that was my opinion based on the way I recall Dokku and Coolify, and a quick scroll through the docs of both, so I might be really wrong here! I definitely need to check out both Dokku and Coolify again sometime.
We support 4 different ones to give folks choice. Some folks want/need features that aren't available on one vs the other (traefik has a ton of features, caddy is simple to configure, nginx has a ton of documentation) so it made sense from that perspective. It was also easy to add once I had the pattern going (though the default has stayed nginx).
One of the main features of Dokku is it's extensibility. You can cut one part out and replace it with another quite easily, and proxying is an example of that. I think that flexibility allows folks to use it in more situations than one otherwise would, though at the cost of being more difficult to maintain (and harder to have cohesion between parts of the system at times).
Re: business model: both Coolify and Dokku are open source, so even if their development stops, you can continue to use them no matter what. (You do have to pay for your own servers though :-) So it's not a PaaS in the traditional sense (like Fly.io or Heroku), but more like “build your own PaaS” thing.