I have written software 10 years ago that has a feature that has now been used by many top brands, and I believe it was the first software tool to feature it. It wasnt patented, but is there any retrospective claim I can make?
I have written software 10 years ago [...]
It wasnt patented, but is there any retrospective claim I can make?
Sorry, but, no, there is no legal claim you can make (at least under U.S. patent law). Only a patent can exclude others from making and using the invention. And you can only file for a patent within one year of the first public disclosure of the invention.
If they stole your actual code (not just the concept), you may have some recourse under copyright law, but that doesn't sound like the situation you are in.