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This site shows you your current system information from your device. Ever wanted to check if you got cookies enabled? Or what browser version your currently running? The reasons you need to know things like that are too many to list, maybe it's because some technical support employee needs to know that from you...
If you are sending a User Agent string, commonly set by your browser, then sysinfox can extract things like it's version, your operating system and device name out of that. The other stuff is JavaScript that runs in your browser.