This version is, as the headline says, just a preview of the coming 3.1, but as stated by Stephen, we get two weeks to report back to him with any problems/issues. If all is quiet at the front, then he will release 3.1 without further changes.
Here’s a short blurb on what OpenToken is:
OpenToken is a token analysis system that is at once powerful, extensible, and easy to use. You should have to do far less work to get a running lexical analyzer or parser than you would with a traditional lerxer/parser generator. In many cases using it is just a matter of picking the right components and plugging them together properly.
Also you might be interested in reading the User’s Guide.