Many countries issue tourist visas as full-page stickers in passports. For example, Canada, USA, Brazil, ... Therefore their visa requirements often state that the applicant is required to have at least one blank page in the passport.
I still have a plenty of space in my passport for stamps, but almost no blank pages as many pages contain only one stamp, so there is not much space for new "sticker visas".
Is it possible to get a visa sticker as a separate document rather than affixed in the passport? I don't have a particular country in mind, this is more a general question. Also, the question is about tourist visas.