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.

Muhr-NumberCruncher-500

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.

Get one at https://www.geekdot.com/numbercruncher-reloaded