Anubis is a partial mitigant of DDOS attacks, since it's less resource intensive to serve the Anubis page than the origin[1].
Cloudflare's captchas are only convenient for a subset of users, I'll bet there'd be decent money in one of the competing CDNs (Fastly maybe?) including an Anubis-like captcha.
[1] : https://news.ycombinator.com/item?id=43864108