The Apache module mod_bwshare throttles HTTP requests to Apache 1 and 2 servers for each client IP address independently. This module accepts or rejects HTTP requests from each client IP address based on past downloads by that client IP address.
If the HTTP client's download rate exceeds specified levels, the reponse to the HTTP client is an HTML warning message. A human browser will see a warning message indicating how long to wait. Automatic rampant downloaders will download large numbers of useless warning messages.
The original motivation for mod_bwshare was to prevent automatic download of all 900 MBytes of material on one of my web sites which was connected to a 33k modem, which would have taken several days if it had succeeded.
Debian Administration site has published the configuration directives for mod_bwshare:
If you're running a popular website you'll most likely notice that some clients are less well-behaved than others. Greedy clients can do anything from make numerous requests, to attempting to spider your entire site.
Avoiding greedy webclients with mod_bwshare [debian-administration.org]