LG has filed a patent for a tri-foldable smartphone/tablet hybrid that also offers stylus support. The device looks like the stuff of dreams for gadget lovers but LG has, to date, indicated that it isn't currently focused on bringing a foldable device to market in the near future.
https://www.notebookcheck.net/LG-patents-imaginative-tri-fold-smartphone-tablet-hybrid-with-stylus-support.434126.0.html