mtar is a simple-ish tool for creating tar files with arbitrary src-to-archive path mappings and regexp filters.
You can download and install mtar using the go tool by running
$ go get -u go.spiff.io/mtar
Usage text can be read at https://godoc.org/go.spiff.io/mtar or by running
mtar -h.
mtar is licensed under the BSD two-clause license. This is readable at the top of its source file(s) and in the LICENSE.txt file.