WordNet sense 1 (fit or ready for use or service):

operable, operational, usable, useable

WordNet sense 2 (ready for service or able to give long service):

serviceable

WordNet sense 3 (concerned with actual use or practice):

practical

WordNet sense 4 ((of e.g. a machine) performing or capable of performing):

operative, running, working

WordNet sense 5 (performing or able to perform its regular function):

functioning

WordNet sense 6 (having a useful function):

useful, utilitarian