Writer.app hasn’t been updated for a little while (as it works just fine on Lion and Mountain Lion and I use it daily), but after reading http://www.guardian.co.uk/books/booksblog/2012/jun/13/write-or-die-app-writers-block I figured I’d write a little ad for Writer.app in the comments:

In the seeming neverending quest to make our computers more like typewriters (and then we regress to, what? Pen and paper? And then chisel and rock?), Writer.app (http://supertart.com/qisoftware/Writer.html) doesn’t let you delete anything. Typing forward? Sure. Pausing for breath without deleting your work? Sure. Bathroom breaks? Okay. Messing around on the internet, searching for pictures of turtles eating bacon? No. Agonizing over edits? Nope.
Might be worth checking out, if you’re into these writer’s sex toys like Written? Kitten. or Write or Die.