NextDNS does a lot more than RethinkDNS, at this point, but no reason why we couldn't implement their feature set. We are a team of three spread thin between the Android app and the stub resolver, but are continuing to make progress. Our focus, unlike NextDNS', is geared more towards anti-censorship.
With RethinkDNS though, right now, you don't need an account and could simply select a set of blocklists and copy the resulting URL to any DoH client [0]. As of today, RethinkDNS, the resolver, is more of a limited BlahDNS / Quad9 replacement than a NextDNS replacement. Limited, because it only supports DNS over HTTPS/[2|3].
That said, we do plan to pick up development pace on the DNS side and FOSS our DNS stub resolver that one could deploy to Cloudflare Workers with one-click [1].
And may be start catching up with NextDNS on the path it has trail-blazed.
Besides, you could use the RethinkDNS Android app to set NextDNS as your resolver instead of the default preset resolver; if you're on Android 8 or below, or need a firewall and on-device DNS logs.
I'm not sure if we'd ever embed the Tor or I2P library in the app (because we'd need to constantly update it with upstream to ensure we don't slip up on security issues), but never say never.
