ssh version 2 "subsystems"

ssh2 supports "subsystems" which apparently means that you can run a
process on the remote server and interact with that process wihtout
prompts.

Openssh supports subsystems via the -s option.

Can someone tell me:
1) What subsystems are supported (Linux and Solaris environment)?
2) How do I use this feature?

I know for instance there is a sftp "subsystem" under openssh and I
have tried:
ssh remote -s sftp

It does not prompt with anything as expected but when I:
put <file>

I expect <file> to be transfered to the remote side but nothing
happens.

Thanks for any insight into this.
.