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Several years ago I owned the domain portscan.io, and I badly regretted letting it expire, as it was purchased immediately by someone else.
But it seems that the current owner has made proper use of it as a free self-scanning service, so honestly, I'm not mad.
I was a bit more selfish with my use of it, and used it to explain to anyone who noticed why I was port scanning the entire IPv4 address space twice per day.