service/donate.md

@@ -1201,3 +1201,8 @@ Giant Rabbit email address and the Tor Project email address
 
 The logging configuration is in:
 `crm-ext-01:/srv/donate.torproject.org/htdocs-prod/src/dependencies.php`.
+
+### Other CAPTCHAs
+
+Tools like [anubis](https://github.com/Xe/x/blob/master/cmd/anubis/README.md), while targeted more at AI scraping bots, could
+be (re)used as a PoW system if our existing one doesn't work.