Notational Velocity is designed exclusively for Mac computers and allows to write notes using only keyboard. You cannot use mouse and will add and search for notes only with keyboard.
Saved notes can be protected with a password. Is a real time application that automatically saves what you type, you don’t need to press any button (save, new note etc.). Can be synchronized with other applications such as Simplenote or Dropbox.
Is formatting text automatically making lists, allows to change order of text to “right to left” (used in some languages), includes a word count and features a few color schemes for interface.