Originally stoacademy.com, with guides, tools, and walkthroughs — including the skill planner a lot of captains had bookmarked. It's back as the STO Academy Build Planner, rebuilt from the ground up and kept current by the community instead of one person alone.
Build Planner — Plan skills, ships, equipment, officers, and traits — then save and share your build.
Combat Log Reader — Upload a combat log and see your DPS and performance stats.
Guides — Practical guides for getting more out of Star Trek Online.