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An open chat server: Website, Wikipedia page

Not free, but there are courses in udemy starting from 15€ for new customers. But be warned, these "basic" courses are between 15 and 25 hours of video. Network is not a topic you can teach yourself in one day.

You can expect a thin client to use about 10 watts idle (but more under load), which adds up to about 100 kWh per year. Some models use even less.

Source,

Thank you for your report 👍

You're right, changes that break compatibility are unlikely. But they can happen and happened in the past (e.g. #3082)

Most of the code is GPL3, but not everything. Source: license.txt

I'm not entirely sure if bitwarden will introduce some changes that break the compatibility with vaultwarden.