A web based XMPP client written in javascript. OTR enabled. Embed in a web page and you're good to go. Can associate with any server you tell it to when you try to log in, so it's not server-specific. Supports all of the important XEP specs.

What seems to be a fairly new web based XMPP client. Owncloud and Nextcloud integrations. Standalone mode also. voice and video enabled, also. OTR enabled. /me emotes.

Jitsi is a F/OSS multiprotocol text chat/voice over IP/video chat application. It supports a large number of instant messaging and VoIP protocols, not only for IM but as transport and control channels for VoIP and video conferencing. If there's a way to get your streams through it'll do it. Natively supports OTR for protecting chats. Implements SRTP and ZRTP for encrypted conferencing. Supports DNSSEC. Aims to replace Skype as a more secure, open source package.

pure-python-otr is just what it says on the tin - it's an implementation of the Off-The-Record messaging protocol in pure Python, meaning that it doesn't hook any libraries that aren't written in Python. Useful for adding OTR support to communications software.