WordNet sense 1 (not busy; not otherwise committed):

uncommitted

WordNet sense 2 (able to act at will; not hampered; not under compulsion or restraint):

free

WordNet sense 3 (convenient for use or disposal):

usable, useable

WordNet sense 4 (free or available for use or disposition):

disposable

WordNet sense 5 ((of especially money) immediately available):

ready

WordNet sense 6 (easily obtained):

accessible