Solution

Schema

// Dropbox, Slack etc.
Table service {
  id integer [primary key, not null, unique]
  name char(128) [not null]
  // OAuth between Rethink Files and e.g. Google Drive
  client_id char(128) [not null]
  client_secret char(128) [not null]
}

// a project can have multiple versions
Table account {
  id integer [primary key, not null, unique]
  name char(128) [not null]
}

// each account has multiple connected services
Table location {
  id integer [primary key, not null, unique]
  account_id int [not null, ref: > account.id]
  // connection to the service
  service_id int [not null, ref: > service.id]
  // username, key
  credential_token char(128) [not null]
  // password, secret
  credential_secret char(128) [not null]
}

// there are multiple ways to implement a folder hierarchy; this is a naive implementation
Table folder {
  id integer [primary key, not null, unique]
  // can be null as the root folder has no parent
  parent_id integer [null, ref: > folder.id]
  location_id integer [not null, ref: > location.id]
}

Table file {
  id integer [primary key, not null, unique]
  // can be null as the root folder has no parent
  folder_id integer [not null, ref: > folder.id]
  // for the sake of completeness, let's normalize the mime type
  mime_type_id integer [not null, ref: > mime_type.id]
  // filename
  name char(255) [not null]
  // "Date Modified"
  modified_at datetime [not null]
  // in bytes
  size integer [not null]
}

Table mime_type {
  id integer [primary key, not null, unique]
  // e.g. application/pdf
  name char(128) [not null]
  // e.g. "PDF document"
  description char(255) [not null]
}

Table favorite {
   id integer [primary key, not null, unique]
   // derived from the screenshot, favorites have a hierarchy 
   parent_id integer [null, ref: > favorite.id]
   // a favorite points to a folder
   folder_id integer [not null, ref: > folder.id]
   // a custom name
   name char(128) [not null]
}