Software that displays a message requesting that the user register it.(noun)
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Use "nagware" in a sentence
"Then your protection turns into 'nagware', bugging you every five minutes until you renew."
"It's hard to find what you want as a downloadable app, plus there's what he calls "nagware": the update reminders, etc. Read the whole story for more."
"VoiceDial is nagware, costing $28 for the full version."