What forum software are you using? For vBulletin, my friend made a free alternative to vBSEO on
vBorg, but I think it's outdated already. Try searching. But really, you should just buy vBSEO as it's the best maintained/supported option.
Though as an aside: vB4, the next major release of vBulletin, will have "human friendly" URLs built in -- so if that's the main reason you want the product you might as well just wait. vBSEO advertises itself as an all-around SEO product, but other than the pretty URLs, it doesn't do much.
When who's online shows bots, it just means the bot is indexing your site. This is a good thing. Most forum softwares have the option to turn these names off, though, so bots just show up as normal "guests." I often do this for new forums so it makes the site seem more active with guests.