What storage adapters are available?

Repository backends currently include:

Backend	Standalone	Drupal
Unix file system	yes	yes
HTTP	yes	coming soon
Amazon S3	yes	coming soon
MySQL	-	yes
PostgreSQL	-	yes
SQLite	-	yes
GDBM	yes	yes
Memcached	yes	-
SFTP	yes	-
FTP	-	-
TFTP	-	-