A comprehensive Qt-based SDK for Matrix development
The Quotient team
Quotient (former QMatrixClient) enables application development for Matrix using Qt. Its two main deliverables are libQuotient, the library to make applications that use Matrix, and Quaternion, the reference client using most of libQuotient. Main features for client development are there, with E2EE and support of full-fledged application services development in the roadmap.
Aside from Quaternion, Quotient code is used by Spectral and a few other clients.
The code, releases and issue trackers can be found in the project's GitHub organisation. Aside from the dedicated Matrix room (see above), news about libQuotient and Quaternion are regularly posted to This Week in Matrix.