RFTagger is freely available but cannot be redistributed.
Copy it to this directory from https://www.cis.uni-muenchen.de/~schmid/tools/RFTagger/ or https://web.archive.org/web/20210928104931/https://www.cis.uni-muenchen.de/~schmid/tools/RFTagger/data/RFTagger.zip and compile it for your operating system according to the instructions in the README of the RFTagger.