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GreenTunnel is a free & open source anti-censorship utility
bypasses DPI (Deep Packet Inspection) systems found in many ISPs (Internet Service Providers)
which block access to certain websites
The app itself is good, but I think GreenTunnel is a bit too heavy (140 MB) as a DNS spoofing app. Also, it requires NetFramework 4.5 too that not everyone has. Another good alternative would be DNSCrypt which is lightweight (less than 10 MB) and already portable.
EDIT: I just tested the app and it doesn't leave any other trace on the system beside %AppData%\greentunnel and %AppData%\green-tunnel. No registry too. I think you can portablize it yourself. Something like:
Use 7-zip (or similar app) to extract installer files without installing it. The green-tunnel-X.X.X-full.nupkg file, to be exact.