I should note, I spent quite a bit of time looking at the official docs and couldn't find an answer for sure right away. It seems like Cloudflare is the only officially supported option (either through the PartyKit managed service or direct).
While I might consider using Cloudflare, I wouldn't be willing to build an app in such a way as to depend on Cloudflare. If Cloudflare changes pricing, or comes under political pressure to terminate my account, or my business changes such that the Cloudflare offering is no longer suitable, I want a way to quickly migrate. It does seem that the main pieces are there and open source, but would likely require some amount of work to figure out and get into production.
While I might consider using Cloudflare, I wouldn't be willing to build an app in such a way as to depend on Cloudflare. If Cloudflare changes pricing, or comes under political pressure to terminate my account, or my business changes such that the Cloudflare offering is no longer suitable, I want a way to quickly migrate. It does seem that the main pieces are there and open source, but would likely require some amount of work to figure out and get into production.