Apps with 'User mentions' feature

Element is a secure collaboration and messaging app based on the Matrix protocol. It’s decentralised to deliver digital sovereignty, and based on an open standard for easy connections and interoperability. It is end-to-end encrypted by default.

XWiki is a powerful Open Source collaborative platform allowing companies of all sizes to save time and money while enhancing collaboration on both team and organizational level.

LOOQME is a full-cycle analytical support for effective communications. Locally and globally.