writerly
I've been using Writerly since long before Google owned it. It's been very useful in allowing my agent and book editors get a look at an early version of something I'm working on without the need for e-mail or snail mail.
It has also proven very handy for allowing magazine editors to get a look at the early version of assigned stories or articles or essays just to make sure we're on the same page before I waste too much time. I get to know what an editor thinks before I do two or three drafts, and I can incorporate the suggested changes much earlier in the process.
I do some original writing on Writerly, but this is not its best use or prime function, at least for me. It's best use is for collaboration, whether with beta readers, agents, or editors.
It could stand some improvements in formatting, but it still works fine flor allowing others to read something you've written, and to offer suggestions.