Syncplay synchronises the position and play state of multiple media players so that the viewers can watch the same thing at the same time. This means that when one person pauses/unpauses playback or seeks (jumps position) within their media player then this will be replicated across all media players connected to the same server and in the same 'room' (viewing session). When a new person joins they will also be synchronised.
CalDAV sync for Android
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Stopped working on it. Doesn't make any sense to spend more time on it; I recommend e.g. DAVdroid as an opensource and ready-to-use solution on clientside.
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For code look at:
https://github.com/e7o-de/android.caldav
UN.me is a web application for both collaboration and general socialization. It synchronizes an environment between two or more users in which they can chat, share photos, collaborate on documents, and more, all in real time.