In the Cisco IOS, PBR is implemented using route maps.
[1] Linux supports multiple routing tables since version 2.2.
[2] FreeBSD supports PBR using either IPFW, IPFilter or OpenBSD's PF.
PBR can be used to redirect traffic to a proxy server by using a PBR-aware L3-switch (router).
In such deployment, specific source traffic (e.g. HTTP, FTP) can be redirected to a cache engine.