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First recommendetion is piwigo, wikipedia.
Next photonix.
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I tried the other suggestions above but I found this guitar tuner that worked nicely. I was even able to accurately hum a range of notes.
https://tuner-online.com/
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Cryptpad by XWiki calls itself the "zero-knowledge cloud". It is more a replacement for encrypted pads, etherpads and Google Docs than for a wiki, but you can use it with some wiki-like features if you have enough discipline (e.g. to cross-link related documents and archive the documents you need)
I'm using it with a few different groups and people ...
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