portguard
portguard is inspired by portsentry, and is similar with portsentry, you can read portsentry's documention to learn more about portguard.
It's written by golang, and the code base is much smaller than portsentry, so you can customize portguard easily as need;
And besides that, portguard's stateEngine is more powerful, it's easy to implement more detection rules.
install
# set GOPATH as need
# export GOPATH=`pwd`
go get -u github.com/xjdrew/portguardplay
launch portguard in debug&tcp mode:
sudo bin/portguard -d -m="tcp" src/github.com/xjdrew/portguard/guard.conf
try shoot your unused port with fun!