cdb - static (constant) databases, opened in read-only mode by the filter : policy database, valid recipients database, bayes database, …
wdb - working databases, where the filter stores live data such as greylisting data, dns resolution, …
ze-greydb - working databases used by ze-greyd (centralized greylisting) daemon;
files - flat text and binary files generated by the filter;
bin - some small tools and scripts useful to manage the filter or the data generated by it;
dbtools - BerkeleyDB tools (ze-db_recover, ze-db_upgrade, …) compiled with the filter and with the same library version of the filter.