Mod name: Guest Sessions mod
Mod version: 0.0.4
phpBB version: 2.0.15 - 2.0.18
Download: click here
edit: temporary download url while phpbb.com is down: files/ca/mod_guestsessions.txt
Description: This mod removes session id from url for guests. This allowes bots (like googlebot) to spider forum correctly without adding session id to urls. And guests won't have more than one session from same ip.