Depends on what type of crypto products you are referring to. If you mean libraries and tools, then Bouncy Castle has implemented it, SunJCE has implemented it, Mozilla has implemented it, CSRTool - an open-source tool for generating Certificate Signing Requests (CSR) uses it, etc.
If you're looking for commercial implementations, then you need to ask the specific vendor(s) of the product you're looking for, to see if they use it. I know of some privately-built applications that use it, but they're not for commercial sale.