At one place I worked around 1991-4, we used them for control hardware for synchrotron beamlines. These were produced in a very small numbers (10s of units) so

At one place I worked around 1991-4, we used them for control hardware for synchrotron beamlines. These were produced in a very small numbers (10s of units) so the cost of the FPGAs wasn't a significant problem, unlike mass market products. At the time we used Altera CPLDs rather than Xilinx. The main differences were: the Xilinx chips needed a small serial ROM located next to the chip to load the bitstream at power-on, whereas the Altera chips used (I guess) some kind of technology similar to EEPROM so they maintained their programming when powered off. The software ecosystem of the two was completely different and a significant lock-in. Once you'd chosen Altera and their Max+Plus II software, the only way to "port" to a Xilinx chip would be to completely reimplement it.