Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
productboard - Beautiful and powerful product management.
Nifty - Manage projects, work, and communications in one place.
FastNetMon - FastNetMon is a very fast DDoS analyzer with sflow/netflow/mirror support.
CAMPR - Open source project management tool with 16 modules
ProdPad - ProdPad helps your team gather ideas, surface the best ones and turn them into product specs, and then put it all on a product roadmap.