Do my collaborators need to signup in order to work on my document?

No - Overleaf is free to use with no signup and no install, just as writeLaTeX was. We hope you like it and choose to signup, but it is not a requirement in order to use the service, either to create documents or to work on those created by others.

If you do invite your friends and colleagues to use Overleaf, you can get extra storage space for free by using our referral offer - once they've signed up, you'll both get 100MB extra space for free as a thank you!