- Dropbox has built an alternative to Google Docs, but cleaner with a better experience. It is integrated deep into your Dropbox Cloud and secure. You can invite folks with a special link to your doc, so they can edit & comment (all optional).
Use Paper to manage technical stuff and my team, and love it. Just the right number of features, document crosslinking and image embedding fits my needs exactly, and works for quick notes or longer documents.
Its a great tool for starters, For teams I do not recommend. there are lots of apps that do the same, even google docs is more intelligible when collaborating and working with. But we already have OneNote, Evernote, Word Online, with lots of features way ahead Paper.
- Big names like Dropbox or Google Docs should be good enough, given you've secured your login credentials with 2-factor authentication etc. They also have dedicated security teams which smaller players may not have. You can add extra security by encrypting your files before putting them in the cloud.