ForFun is a database of linguistic forms and their syntactic functions built with the use of the multi-layer annotated corpora of Czech, the Prague Dependency Treebanks. The purpose of the Prague Database of Forms and Functions (ForFun) is to help the linguists to study the form-function relation, which we assume to be one of the principal tasks of both theoretical linguistics and natural language processing. A prototypical question to be asked is What purposes does a preposition 'po' serve for or What are the linguistic means in the sentence that can express the meaning 'a destination of an action'?. There are almost 1500 distinct forms (besides the 'po' preposition) and 65 distinct functions (besides the 'destination').