Custom private blockchain with PHP implementation (using a relation DBMS).
-Centralization -Complete transparency -Complete proof of work -ability to hide/show block values
The blockchain is stored in a central server, clients can only view the complete blockchain and add a block. When a client add a block, he can choose between show immediately the value or not, in any case clients can hide/show their values in their block in any moment. The value in a block is hashed and stored in a variable called ValueHashed, which is always shown.
Value: text of the value
ValueHashed: sha256(Value)
TimeStamp: date of the timestamp of the block
Hash: sha256(ValueHashed + TimeStamp + prev Hash)
see also a web implementation http://proofit.ml/