sxmppd is a server for the XMPP (Jabber) chat protocol. While other, functional XMPP servers exist, they are not as simple or have many dependencies. It supports user authentication, SSL, roster management, presence updates and subscriptions, messaging (local users), group chat, and file-based server configuration.
SMStoXMPP is a lightweight PHP-based SMS to XMPP bi-directional gateway application which receives messages from an SMS gateway device/application and relays them to the target user via XMPP. Replies to the user can be made via XMPP, which then delivers the message back to the SMS gateway.
SecuXabber is a secure Jabber-client for Android that uses strong, asymmetric encryption on top of the XMPP protocol. A key pair is generated on application start-up. Users can send their public key to other SecuXabber users via Bluetooth. This face-to-face check ensures the veracity of the public key. After the keys have been imported by both users, all communication between them is encrypted using strong 4096 bit encryption. It supports all relevant XMPP features, works with multiple accounts, is highly customizable, and has many other useful features.