golangy
Structured logging, metrics, and tracing.
zap
Structured, leveled logging built for speed — the usual answer when slog's standard-library defaults aren't fast enough.
zerolog
Zero-allocation structured logging with a chainable API — zap's main rival, and slightly friendlier to read.
OpenTelemetry Go
The vendor-neutral tracing and metrics SDK — the safe default when you don't already know which observability backend you'll end up on.