i made a blockchain in under 20 lines of bash. here it is. you can store arbitratry messages in this blockchain. it adds 4 bit of pow for each message.
# usage ./list.sh "message"
f=list.txt
maxlen=100
hashp=""
while [ "`echo "$hashp" | cut -c -1`" != "0" ]
do
let n++
hashp=`(echo "$(tail -n 1 $f | cut -c -500)$n" ) | shasum -a 256 | grep -Po "^\S+"`
done
hashc=$(echo "$@" | shasum -a 256 | grep -Po "^\S+")
c=$( tail -n $maxlen $f; echo "$hashp $hashc $n $@" )
echo "$c" | tee $f