Psi is a cross-platform powerful XMPP client designed for experienced users. User interface of program is very flexible in customization. For example, there are "multi windows" and "all in one" modes, support of different iconsets and themes. Psi supports file sharing and audio/video calls. Security is also a major consideration, and Psi provides it for both client-to-server (TLS) and client-to-client (OpenPGP, OTR, OMEMO) via appropriate plugins.

Psi+ is a development branch of Psi with rolling release development model. Users who wants to receive new features and bug fixes very quickly may use Psi+ on daily basis. Users who do not care about new trends and prefer constancy may choose Psi as it uses classical development model and its releases are quite rare.

List of supported XEPs you may found at: https://github.com/psi-im/psi/wiki/Supported-XEPs