Recently I watched again the Star Trek film Insurrection. This will not be a movie review. In the film, there was a space battle scene in which the enemies of the Enterprise used an "isolytic burst" weapon. The Enterprise crew were surprised, as the weapon was banned by some treaty or other, for being unpredictable. I think it was supposed to be a scene to show how the Enterprise crew are creative and resourceful thinkers. Maybe it worked at that, maybe not. Watch the film and judge for yourself.
We never actually see what the weapon is supposed to do. Rather we get told about it by several crewmen, and then the Enterprise defeats it, and the enemies. The weapon might as well have been a 20th century ICBM, or a boring old laser beam.
So I thought, what kinds of crazy weapons could show up in my TU, as unique and probably banned weapons?
Well, there is the "stellar ray" from that post on Edmund Hamilton's "Crashing Suns". That's a crazy-powerful weapon.
Here are some of the unusual and illegal weapons that have been at least researched if not developed by star nations in my TU. The Talaveran Empire has declared a ban on all of them; any vessel found in Imperial Space equipped with such will be impounded and destroyed, or just destroyed if they don't surrender.
"The Imperial Ministry of Defense in conjunction with the Ministries of State and of Science have signed resolutions, later confirmed by the King, banning the experimentation, development production or use of the following devices. Some of these were explored by the Ministry of Defense, but were rejected by the Navy as being “irresponsible, inhumane and contrary to the ways of civilized peoples”."