Instruments

Instruments are found as rewards for getting enough achievements. Although they don't serve any combat purpose, you'll be able to play music for you and your fellow explorers.

The instruments that utilize the Playable Instruments add-on (must be installed to use) are...

Flute
Clarinet
French Horn
Standup Bass
Orchestral Violin
Keytar - Capable of playing Bass, Clarinet, Flute, Frenchhorn, Gameboy, Guitar, Piano, Strings, and Synth, but only one at a time.

You can also sync these instruments with another player's instrument by using the /sync command.

Maxwell the playable cat - An event exclusive item. Requires extreme finesse to use.

Other instruments that don't utilize the Playable Instruments add-on...

Bugle - Makes a honking noise whenever the player clicks.
Boombox - Boombox is only usable by donators that have donated $12 USD or more. Here is a list of songs playable on the Boombox.