We recently had a request to set up a SharePoint environment to serve as a less featured version of a virtual data room so that an organization could make available documents to external users and organizations. SharePoint was chosen as the environment by the client because of the relative speed in which the needed components could be set up.
In this particular case, the client needed various other organizations to access certain files they would make available for a short amount of time. Rather than setting up a dropbox and going through the motions of inviting users to it and worrying about limitations imposed by drop box, the team asked us to spin up a SharePoint site for the purpose of sharing the files.
A single document library was created with the necessary folders for each outside organization. Access to each folder was granted to a corresponding group, so that each user into the system would only see their folder. The client could then drop the correct documents into each organization folder, and then simply invite those external users into the site and into the corresponding group.
This was set up in half a day and required minimal training to the client. External sharing in SharePoint and Office 365 is the driving force behind this particular solution. For this particular case, the invited users only needed a Microsoft account of some kind whether that be another Office 365 account, or an outlook account. More information on external sharing can be found here https://support.office.com/en-us/article/external-sharing-overview-c8a462eb-0723-4b0b-8d0a-70feafe4be85.