growthcoin from what i know. hbn im not too sure of. theres others i just dont remember from the top of my head
It seems you are wrong with Growthcoin: It contains the code for the centralized checkpoint system - look at checkpoints.h after
// ppcoin: synchronized checkpoint
class CUnsignedSyncCheckpoint
Source:
Growthcoin repoPS:
Hobonickels has the checkpoint system too.