Bundeswehr uses instant messaging – Matrix

BWI currently operates two chat solutions for the Bundeswehr for official and private mobile devices: Matrix and stashcat.
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In the course of further expansion, Matrix will replace stashcat as the federal armed forces’ standardised instant messaging platform.

https://www.bwi.de/news-blog/news/artikel/kommunikation-in-covid-19-zeiten-bundeswehr-setzt-instant-messaging-ein