@mcc@mastodon.social we've been using Nextcloud calendar sync for ~6 years for our coöp work, and some of us use the contact sync personally: works great! Sync is based on the open CalDAV/CardDAV standards, which on Android (weirdly) requires an app, we recommend https://www.davx5.com/ It's got some overlap with MS Exchange, but focusses more on files than e-mail (Dropbox-style file sync is still probably Nextcloud's main strength). History-wise, Nextcloud was a fork/re-do of Owncloud, which started around 2010, whereas Exchange has been around in various forms since 1996. Nextcloud is federated – Cooperative.computer users can share files, calendars etc. with folks on other Nextcloud servers, but as far as I know it's not directly integrated with Matrix. Hope this helps, fire more questions at us if you have them! ♥ – 3wc