Axel Muhr has just released a Floating Point Unit interface card for the Apple IIgs and Apple IIe (enhanced and unenhanced). The NumberCruncher Reloaded is a peripheral card for the Apple II series that features a math co-processor, often also called a Floating Point Unit (FPU) which is specialized on, well, floating point calculations. Doing so, it is much, much faster than any 6502 or 65816 CPU ever will be.
That said, the NumberCruncher Reloaded will not automatically speed-up your programs as CPU accelerators like the Transwarp GS or ZIP CHIP would do. Programs will have to be either specifically written to use the NumberCruncher Reloaded or use a floating-point library like the SANE interface which then needs to be patched to itself use the NumberCruncher Reloaded for calculations instead of the main CPU.