If you want the latest bugfixes (or bugs...), you can grab one of these nightly snapshots (in principle, these have the same content as regular releases, but they are extracted automatically every night from the source code repository). Since the generation of the snapshots is an automated process, there is no guarantee that they will work. But normally, they should work.
 

Weka snapshots

 
developer-branch.zip(45M)
stable-3-6.zip(24M)
stable-3-8.zip(44M)

Updated  Tue May 9 14:05:52 NZST 2017

If you encounter any problems then please contact: mhall at cs.waikato.ac.nz