The contra alto flute is in the key of G (or sometimes F), pitched one octave below the alto flute - which is a fourth lower than the concert flute. The instrument's body is sometimes held vertically, with an adjustable floor peg similar to that of the bass clarinet. But, it is sometimes held horizontally. It just depends on the company.
The instrument maker Eva Kingma calls her contra-alto flute a "contr'alto flute in G," and Kotato & Fukushima call their instrument "bass flute in F." Kotato & Fukushima's instrument sells for US$17,500.
For an extensive list of repertoire for bass flute and contrabass flute see: Peter van Munster, Repertoire Catalogue for Piccolo, Alto Flute and Bass Flute, Roma: Riverberi Sonori, 2004.
More and more flute ensemble repertoire is incorporating the contra-alto flute. Typically, it is doubled with the contrabass (and/or bass) flutes, however, in recent years, composers and arrangers such as Alexandra Molnar-Suhajda and Judy Nishimura have been pushing the boundaries of lowness by writing independent parts for the instrument.