What do you want to develop for Zenoss Core?

Agent monitoring - support of active mode (agent is sending data to Zenoss server) https://github.com/jangaraj/ZenPacks.JanGaraj.ZabbixAgent

Skyline integration - dynamic thresholds (no holt winter algorithm) https://github.com/jangaraj/serviced-app-skyline

PHP Network Weathermap - fancy maps with metric values https://github.com/jangaraj/serviced-app-zenoss5-network-weathermap

Others - please post your idea to forum http://www.zenoss.org/forum/9301