Loggr vs Zap: What are the differences?

Loggr: Monitor Your Web Apps in Realtime. Get a control panel for your web app with event logging, user monitoring, analytics, notifications and more; Zap: Blazing fast, structured, leveled logging in Go (by Uber). Zap takes a different approach. It includes a reflection-free, zero-allocation JSON encoder, and the base Logger strives to avoid serialization overhead and allocations wherever possible. By building the high-level SugaredLogger on that foundation, zap lets users choose when they need to count every allocation and when they'd prefer a more familiar, loosely typed API.

Loggr and Zap can be categorized as "Logging" tools.

Zap is an open source tool with 7.22K GitHub stars and 553 GitHub forks. Here's a link to Zap's open source repository on GitHub.