Connection Managers
Connection Managers are the components responsible for actually connecting to the Jabber/AIM/... server. Your distribution probably has packages for most or all of the current CMs, so you don't need to install from source unless you're on a weird distro or want to hack on them.
Stable
Gabble: A Jabber/XMPP connection manager that handles single- and multi-user chats and voice/video calls.
git clone git://anongit.freedesktop.org/telepathy/telepathy-gabble
Salut: A link-local XMPP connection manager (XEP-0174). CategorySalut
git clone git://anongit.freedesktop.org/telepathy/telepathy-salut
Idle: A IRC connection manager.
git clone git://anongit.freedesktop.org/telepathy/telepathy-idle
Rakia: A SIP connection manager based around the Sofia-SIP library (formerly known as Telepathy-SofiaSIP)
git clone git://anongit.freedesktop.org/telepathy/telepathy-rakia
Releases (source code, development branch only); stable and historical releases can be found under the old name, and yet older ones on the SF.net project page.
Under Development
Haze: A connection manager based on Pidgin's libpurple, supporting all protocols in Pidgin (AIM, ICQ, Yahoo, MSN, etc) at a basic level, but already very usable.
Releases (source code); new releases are announced on the Telepathy mailing list.
git clone git://anongit.freedesktop.org/telepathy/telepathy-haze
Requires libpurple and Telepathy GLib
Butterfly: An MSN connection manager that handles presence, conversations, avatars, personal messages, server-side aliases, and full contact management (including groups).
git clone git://anongit.freedesktop.org/telepathy/telepathy-butterfly
Requires Papyon and Telepathy Python.
telepathy-ring: GSM support via Ofono.
Sunshine: A connection manager with support for Gadu-Gadu network that handles basic GG 10 protocol features.
git clone git://anongit.freedesktop.org/telepathy/telepathy-sunshine
Requires Twisted Framework and Telepathy Python.
telepathy-mixer: support for the MXit protocol.
Dead
Wilde: An AOL/ICQ (Oscar) connection manager, this handles single direct messaging, presence, conversations and simple buddy list (add/remove). OscarSOC
Clients
As a user, you interact with a Telepathy Client.
Empathy: a Gnome IM/voice/video client reusing Gossip's UI and using Nokia's Mission Control
KDE-Telepathy: a collection of components providing IM capabilities to the KDE desktops
The instant messaging, address book and VoIP user interfaces on Nokia's Maemo-powered internet tablets/phones (such as the N810 and N900) are Telepathy clients.
Many OLPC activities do collaboration using telepathy, including Paint and Chat.
Dead
These clients are unmaintained, as far as we can tell, and are only included here to warn unwitting users against using them.
Ereseva: VOIP-capable webphone, based on tapioca-python and GTK+ libraries. (Ereseva SVN repository)
Landell: a GNOME Instant Messenger built around Tapioca# (C#/Mono)
Cohoba: a UI for GNOME desktops by Raphaël Slinckx (Python)
GnomeUI: an experimental UI for Gnome desktops by Adam Lofts (C#/Mono)
Banter: a Gnome IM/voice/video client with a rich user interface (C#/Mono)
Tools
Telepathy Inspector: A telepathy client (GTK+) whose objective is to expose all interfaces and functionalities implemented by a given connection manager along with its connections, channels, etc.
Libraries
Telepathy GLib: A GLib/GObject-based library for clients and connection managers
Telepathy-Qt4: Qt4 library for use in Telepathy clients, including a Qt binding for Telepathy-Farsight
Telepathy Python: Python libraries for use in Telepathy clients (e.g. Cohoba) and connection managers (e.g. Butterfly)
Telepathy-Farsight: a GLib/GObject library that uses Farsight2 to handle the streaming part of media streaming for channels with the MediaSignalling interface
Wocky: an XMPP library that is built entirely asynchronously, makes it easier to provide more modern XMPP features, and takes advantage of the latest GLib features, such as gnio. Wocky source is directly in the gabble tree (via a git submodule).
Older libraries
These libraries are not up to date with current versions of telepathy-spec. They should not be used.
TelepathySharp: A .NET library for use in Telepathy clients
TapiocaSharp: A high-level .NET library on top of TelepathySharp for use in Telepathy clients (e.g. landell)
TelepathyQt: Older Qt4 libraries for use in Telepathy clients and connection managers
TapiocaQt: A high-level Qt4 library on top of TelepathyQt for use in Telepathy clients (e.g. decibel, kopete)
libtelepathy: A GLib library to ease writing Telepathy clients in glib; deprecated in favour of Telepathy GLib. releases
Other Components
Mission Control: an Account Manager and Channel Dispatcher implementation, which stores accounts and coordinates the launching of connection managers and clients.
Stream engine: The part of the Maemo UI that handles the streaming aspects of a Telepathy client, it uses Telepathy-Farsight, Farsight2 and GStreamer to handle media streaming for channels with the MediaSignalling interface.
telepathy-feed: A Galago feed for Telepathy. http://telepathy.freedesktop.org/releases/telepathy-feed