I own a Synology DS409slim on which I have enabled SSH. The primary idea was just to have a look behind the hoods. This is quite simple: browse to the configuration panel, select the terminal services section and active the SSH daemon.
But once there, you’re stuck with a basic shell and a few commands. No `less`, no `grep`, no `bzip2`, no `perl`… Synology provides an official packages repository that provides a few extra features ; like VPN, LDAP and such ; but not so much to get a “complete” UNIX environment. The savior here is called “ipkg”. Quoting Wikipedia: “(…) the Itsy Package Management System (ipkg), is a lightweight package management system designed for embedded devices that resembled Debian’s dpkg. (…)”. It provides a bunch a GNU-like tools and it runs on the Synology!