museum piece

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. One that is worth keeping or showing in a museum.
2. n. One that is old-fashioned: "[The show] is a living museum piece, a piece of Americana from another era” ( Patti Hartigan).

Wiktionary

1. n. slang a very old item.
2. n. informal an obsolete form of technology