Box - Box external drive
Dropbox - Dropbox external drive
IMAP - IMAP mail box
GDrive - Google Drive external drive
RACKSPACE - RACKSPACE external drive
S3 - Amazon S3 external drive
SkyDrive - SkyDrive external drive
Share - Shared resources
WebDAV - WebDAV external drive
CardDAV - WebDAV CardDAV extension (RFC 6352)
CalDAV - WebDAV CalDAV extension (RFC 4791)
DynamicResource or DR - a store for dynamic SQL queries (in particular SPARQL)
LinkedDataImport or LDI - import RDF data in an internal RDF graph
SocialNetwork or SN - Social Networks external drives: Twitter, Facebook, LinkedIn, WordPress, Google+
FTP - FTP external drive (passive mode)