KnowledgeTree Open Source Edition version 3.5 and onwards is licensed under the GNU GPL version 3. The GNU GPL version 3 is an Open Source Initiative-approved license.

KnowledgeTree Open Source Edition version 3.1 to 3.4 are licensed under the KnowledgeTree Public License.

Earlier versions of KnowledgeTree Open Source were licensed under the GNU General Public License version 2.0.