Will Bakker -- A concertina is a "squeezebox," a small instrument in the accordion family. There are lots and lots of styles and key arrangements.
My main instrument for the past nine years has been a chromatic zither, beautiful with a full rich sound but damn near impossible to play, for the first three years or so. Also impossible to bring up to pitch unless the zither is in a good mood.... See photo on Bill D's site once he actually gets on line with the pics. Second instrument, also on Bill's site, a MacArthur harp. Diatonic, not chromatic, only about 1/10 as hard to play as the zither. Have two guitars, a Martin D-28 and a Gurian Jumbo Rosewood.
Since I got the above instruments I've done lots of 19th century parlor songs and simple bouncy things like the Glendy Burke, for the little harp. But I'll sing anything, pop, folk, ballads, sea chanties, cowboy songs, country, international folk, opera (but never when anyone is listening), musical comedy, well -- you get the idea.
I, too, want to do some singing in old folks' homes. They're a very appreciative audience! -- have plans to do an hour for St Patrick's Day.