Late Medival Era: Religious music continued to develop the concept of harmony, eventually extending to four or more vocal parts. Unlike modern western music, songs were expected to end with all parts in unison on the root. So, if a song was in the key of C (though the idea of a key was still not developed), all voice parts would end on a C. This eventually broadened to encompass ending on any 'perfect chord' (perfect chords: unison, octave, 5th, 4th. Imperfect chords (which were allowed, but not to begin or end a phrase): M3, m3, M6, m6. Dissonances (which were not allowed, except as passing notes (to transition from one chord to another)): m2, M2, TT (tritone), m7, M7). This era also saw the development of keyboards as instruments capable of playing multiple notes (Keyboard instruments had existed earlier, but were relatively uncommon and only used to play a single note at a time, in most cases). However, religious music still mostly limited keyboard instruments to practice tools, and performances remained the domain of the a cappella choir.
Popular music, meanwhile, had explored and inhanced the concepts of harmony developed by sacred music. Performances including multiple instruments/instrument and voice were now the exception, rather than the rule. Simple percussion was still the norm (little changed from roman times), but it was during this era that pitched percussion (hand chimes, most likely) is believed to have first developed. Metalic horns were also present in this era, but fingered horns would not come into play until the 1700s. Woodwinds were still common, and the forerunners to the clarenet and oboe were already present.
(Incidentally, I consider this the most facinating musical era. It was a period when western civilization was exploring what it meant for something to be 'music,' and the level of artistic innovation present at this time has, imho, never been equaled.