It may be possible to use gravitational waves to transmit signals, although gravity is hugely more challenging to manipulate than electromagnetism because it's

It may be possible to use gravitational waves to transmit signals, although gravity is hugely more challenging to manipulate than electromagnetism because it's purely attractive and interacts much less strongly with matter, making this very unlikely in my opinion. Another theoretically plausible but very unlikely signal carrier could be neutrinos. 'Tachyon' is a name used to refer to any theoretical particle which travels faster than the speed of light; as far as I'm aware all current experimental evidence rules out the existence of tachyons.