what is a good example of a decomposer?

bacteria / fungi

Depends on context

Merriam-Webster defines as any of various organisms (as many bacteria and fungi) that return constituents of organic substances to ecological cycles by feeding on and breaking down dead protoplasm

From http://www.replayinc.com/Products/Decomposer.htm

DeComposer is an advanced filtering program that allows you to filter out a single instrument or sections of instruments from any digital audio file. Just imagine that you had a digital audio file (herein referred to as a wav file) of a great guitar solo and you wanted to hear yourself playing that solo instead of the recorded artist. Just set up the DeComposer note filter to take out the guitar from the mix and its gone. Now you can play the solo yourself, using all of the other original band members as your own personal backing band.

I could go on.

An organism that breaks down the bodies or parts of dead plant or animal matter into smaller pieces (decay). Decomposers, such as mushrooms, bacteria, and earthworms, are very important in food webs.

www.fcps.k12.va.us/StratfordLandingES/Ecology/mpages/glossary.htm

Mushrooms

bacteria, fungi, actinomycetes

“Bacteria”