Recs.
Updated
Specs
Pros
Pro Amazing mobile interface
Unlike other mobile apps, Quip has really innovated with the text editor on mobile. They have a great interface for formatting text that stays out of your road to maximise how much room you have to type.
Pro Lots of features
Quip has loads of features both on the sharing front and the editing front.
Pro Great editor
The editing experience in Quip is quite nuanced and pleasant. There is markdown support that formats as it is typed as well as support for checklists and the ability to make hierarchical lists. There are also controls for formatting in the UI, so it is all easily accessible.
Pro Private document sharing
Files can be shared with others via a URL. The owner of the shared document can set it to be in read-only mode or they can allow anyone to edit it. Collaborators don't need to have a Quip account to participate. This feature makes for a great Evernote alternative, for those looking for a different app that has this similar function.
Cons
Con Not really free with stringent controls on trial
The trial is content limited which means if you start using it quite a bit they'll pick the perfect moment to swoop in and start charging you. It's better for them because it means they can look at your account and pick the best time to ask you to pay (hey we notice you're using Quip lots and have a new project you just started how about you pay now or you lose everything).