SàT is multi-frontends: the heart of the software is independant from its view, that mean that you can have differents interfaces adapted to specifics usages.
Share your thought either publicly and privatly (see below), thanks to the microblogging feature. With the decentralised nature of XMPP, you don't have to rely on one specific server, so you can stay master of your data, and avoir censorship.
Keep access to private data only for the people you choose. SàT use groups to manage your permissions, and avoid your coworker to see your party pictures.
Advanced chat and group chat
XMPP is one of the best (and probably the best) instant messaging protocole ever made. There are plenty of things you can do, far too much to detail everything here. In addition, you can join muli-user room, and discuss with tons of people.
With XMPP, you are not limited to chat or short messages: you have no size limit, and if you want to write essays or to highly detail your last holidays, you can.
Communicate with other networks using different protocoles. with SàT and XMPP, you'll not stay behind closed walls.
Easily send file to your friends.
Play with your friends or other people
Thanks to it's IMAP/SMTP plugin, you can use any e-mail client to communicate through SàT. Combinate this with the gateway feature, and you can send message with it to any network (including traditional e-mail netwwork). One of the goal of SàT is to allow easy transition to Jabber as an alternative to classical e-mail network, with a better protection to SPAM and identity spoofing.
This is a feature for power-user: SàT allow to send command-line tools' stdout to your contacts. This actually is as easy as knowing the name of your contact.
An other feature for power-user: you can export input/outputs of an Unix CLI command to any contact (using any XMPP client or even other protocols through gateways).
Experiment music with your friends: in a multi-user room, you share a playlist; everybody can add songs to it, and everybody listen the same music at the same time. Good way to share your taste and discover new songs.
Not exactly a feature, but certainly one of the most important point: a social contract
has been written as a moral engagement around the project. SàT is not made for money or trap people, it's a project about freedom and sharing.