| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| go/token | Package token defines constants representing the lexical tokens of the Go programming language and basic operations on tokens (printing, predicates). |
| sort | Package sort provides primitives for sorting slices and user-defined collections. |
| sync | Package sync provides basic synchronization primitives such as mutual exclusion locks. |
| unsafe | Package unsafe contains operations that step around the type safety of Go programs. |