The Gemini Observatory pursues an unusual concept. It operates two similar 8.19 m telescopes. One is located on Mauna Kea in Hawaii (Gemini North), the other on Cerro (Gemini South), together covering almost the complete sky on both hemispheres.
Image source: http://www.physics.unlv.edu/~jeffery/astro/telescope/gemini_north_sunset.jpg
The observatory is operated by an international partnership currently consisting Argentina, Australia, Brazil, Canada, Chile, the United Kingdom, and the United States.