What standard libraries or packages have you used in your practice?

In practice, the following standard libraries are often used in Go:

• fmt — for formatted input and output.
• net/http — for creating HTTP servers and clients.
• encoding/json — for working with JSON.
• io and io/ioutil — for working with streams and files.
• os — for interacting with the operating system (files, environment variables).
• time — for working with date and time.
• context — for managing request lifetimes and canceling operations.
• sync — for synchronizing goroutines.

Example of using append for slices:

slice := []int{1, 2, 3}
slice = append(slice, 4, 5)
fmt.Println(slice) // [1 2 3 4 5]