There is no "free" version of Brother's Keeper.
The program is shareware, with some features not being unlocked until the program is registered and paid for.
What specific version of BK are you using? Current version is 6.2.80 as of 24 August 2008
REF Number and REF Date are event fields.
I presume it's used to keep BK entries in comparision with index numbers generated by other genealogy programs or with other numbering systems. For example if you imported a GEDCOM from Family Tree Maker, the GEDCOM would include an index number for each individual based upon FTM's program. That would be the REF number. You could look at the ref number report and compare it to the FTM database and ensure you got the correct person. Since names can be common, and you might not have enough date info, it helps prevent errors.
The equivilent report in BK would be BK Number.