Ficelle chair by Osko and Deichmann for Ligne Roset
The chairs designed by Kazuyo Sejima+Ryue Nishizawa/SANAA are actually called Armless Chair and Armless Chair (Wide), part of Maruni's Nextmaruni concept line. The idea behind them (literally) is that the portion of the chair back aligned with the spine is removed, making the chair more comfortable by reducing pressure on the spine.
Anonymous; Enameled Metal 'Sekitei' Chair by Nendo for Cappellini, 2011.
Greyhound Dog Chair
Chair | Marcel Breuer | Bauhaus
675 chair by Robin Day - Britain Can Make It
Nendo - heel chair
SaloneSatellite at Milan Design Week
223 From SaloneSatellite - A chair and footstool from Rui Alves, who works under the title My Own Super Studio which he founded in 2001. He is a third generation craftsman, and says his “mind is always working on creating or disassembling something.”