SplitsTree App - download page

Program installers:

SplitsTree_macos_6_4_7.dmg (MacOS X)
SplitsTree_windows-x64_6_4_7.exe (Windows)
SplitsTree_unix_6_4_7.sh (Linux or unix)

A user manual can be found here.
Use this file in find similar tab of analyze genomes dialog as database file (unzip first):
gtdb_rep_k21_s1000.db.zip
To find out what has changed in recent versions, see the release notes.
Use this file to check MD5 checksums for the installers: md5sums.txt.