Scientists have grown functional mouse sperm from embryonic stem cells in a lab and used it to make healthy mice. The team in China are now hoping to be able to repeat it with stem cells from an adult donor.
This would allow men who don't produce sperm or who's sperm is extremely low quality to father biological children. Oh, and there's no reason it wouldn't work for trans men - or even women who want to have biological offspring with a same sex partner.
Eggs, of course, are a lot more tricky to cook up.