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https://archive.tibco.com/ – Search for "Jaspersoft Studio 6.6.0". You need a free TIBCO community account. jaspersoft studio 660 download link
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Once you have the correct and the installer: long since inactive
He found a forum post from 2019. A user, long since inactive, had asked the same question. “Where is the standalone installer?” The reply was dismissive. “Use the marketplace.”