WordNet sense 1 (said or done without having been planned or written in advance):

spontaneous, unwritten

WordNet sense 2 (not furnished with or using a script):

unscripted

WordNet sense 3 (with little or no preparation or forethought):

extemporaneous, extempore, impromptu, off-the-cuff, offhand, offhanded, unrehearsed, extemporary, offhand

WordNet sense 4 (without preparation; not prepared for):

unprepared

WordNet sense 5 (perform without preparation):

extemporize, improvise, extemporise, improvize