TheRarestWords is an interesting Russian-developed project that seems to have the goal of optimizing search engine results by pulling out the rarest words on any given site. Basically, TheRarestWords bot scours the internet, examines words on URLs and then lists off the rarest words found on each site. The thinking behind this appears to be that having rarely used words will help you be found faster when people type in those exact words into their search. The homepage of TheRarestWords allows you to scan through the sites that the bot has visited and then write up a one-hundred character definition of any of these words. The idea behind this is that by defining the word, it will give it an edge in future semantic search endeavors. There are a number of other options on the site and it takes a bit of reading to understand it well, but it is worth a visit.