I had a similar problem and downloaded the jar from http://mvnrepository.com/artifact/org.freemarker/freemarker which worked out well.
When you take a look at build.gradle in the DaoGenerator-project, you'll find a dependency that points exactly to this artifact. I guess using gradle to build your project automatically downloads these dependencies just like maven does. If you do not wish to use either, it's probably fine to download and include the artifacts manually.