SEAddon is still in closed development.
It is intended to be the replacement for F2PAddon, which was created primarily to allow users of Starter Edition accounts to both chat and form groups with each other, although it has been expanded over time to provide a few other features useful to S.E. players.
The major difference between the two will be that SEAddon no longer requires players to be in your friends list in order to chat with them. However, this is such a major change that the addon will need to be rewritten from scratch.