An incredibly simple commandline tool that outputes the date and time in RFC3339. The name isodate comes from iso 8601. If you want to know the differences between the RFC and ISO spec, check out https://ijmacd.github.io/rfc3339-iso8601/.
We use Go's hardcoded definition of RFC3339, as seen at https://pkg.go.dev/time#pkg-constants
$ go install github.com/icco/isodate@latest