Simantra (or semantron or in Romanian Toacă) is an Eastern Orthodox percussion instrument used in liturgical service and is either a wooden or metal slab or bar that is mounted or suspended and struck with a mallet. The Simantra has been used by classical composers including Iannis Xenakis (Persephassa) and in Michael Gordon's Timber (2011). A Simantra is rich in overtones compared to the bars of percussion instruments such as a marimba or xylophone, where the fundamental is primary. The tone changes based on how near or far from the nodes the mallets strike the board.
For the history of the instrument, see the much more detailed article for the Semantron.