Possible Clues:

• Glockenspiels' kin
• Relatives of pianos
• Keyboard instruments that sound like glockenspiels
• Instruments that sound similar to glockenspiels
• Set scale differently for these instruments
• Instruments featured in Tchaikovsky's 'Dance of the Sugarplum Fairy' and the Velvet Underground's 'Sunday Morning'
• Some metallophones