NorthStar - FPB-A
This was the first S-100 board NorthStar ever made. Clearly a specilized board but very useful in certain applications.

The North Star hardware floating point board (FPB-A) was a single S-100 bus circuit board which performed floating point add, subtract, multiply and divide with up to 14 digits of precision. The FPB performed floating point operations approximately 25 times faster than the best Z80A software or firmware. A typical 10 digit multipli­cation, when performed by the FPB, computed in 111 micro­seconds. The time was 2.7 milliseconds when the same operation is performed by the best Z80A software. Number representation for arguments and results are BCD (binary-coded-decimal).
  
The FPB implements a high-speed micro-programmed processor specially designed to perform fast floating point arithmetic. The FPB waited for a command from the Z80A or 8080 program to start a floating point calculation. The command indicated both the operation desired and the precision. Then the FPB received the floating point values one byte (two digits) at a time, computed the result, and returned the result along with a status byte indicating any overflow or underflow conditions. The method of communication between the FPB and computer permitted values to be passed at the rate of 3 microseconds per byte using a Z80A, and proportionately slower if a lesser speed computer was used. A version of BASIC which uses the FPB was provided with NorthStar's Horizon and Micro-Disk Systems. Use of the FPB could speed up NorthStar's BASIC by as much as a factor of 10 when extensive mathematical calculations were being performed.   
 
The manual for this interesting board can be obtained here.