Jmol is free software. You can download it, use it, redistribute it, etc. without paying anything.
Jmol is open-source. This means you can obtain the source code and even change it, under the terms of the license, described below.
Jmol is offered under the LGPL License (GNU Lesser General Public License).
JSmol is a part of the Jmol product, hence subject to the same terms.
Licenses when using JmolApplet in webpages
JSmol Library (including JSmol.min.js and other files)
JmolApi.js, JmolApplet.js, JmolControls.js, JmolCore.js Libraries
These new libraries, also meant for insertion of JmolApplets into webpages, are equally covered by LGPL.