There's also
this old thing. For 68K Amigas only, though. Only slightly more secure than a startup-sequence password prompt.
Envoy, the networking package, also had some limited security features, but I think they only work via remotely shared devices, not for users on the local machine.
On the hardware side, there's
this, which should prevent access to the system as long as you can prevent someone from opening your machine. I think the newer Flash ROM cards can do something similar.
Basically, the most secure a maximally-secured Amiga can be is "can prevent someone from accidentally moving/deleting something, maybe." A moderately experienced user could bypass anything currently available with little effort. The good news for most of us is that almost anyone other than ourselves who might be using our Amigas is not going to be a moderately experienced user
