* Experimental processor design. If you want to make a processor with its own custom instruction set, or modify an existing processor design, you need an FPGA to actually see it in action.
* Synthesizers and audio filters. You can do a lot of low latency signal processing compared to even a beefy microcontroller with an FPGA, so if you want to make your own synth sounds in hardware, an FPGA might make sense.
* Computer vision stuff. If you want to make some gadget that does some kind of image processing that is streaming from a camera, and FPGA would work, especially if you wanted it to be small/portable.
* Experimental processor design. If you want to make a processor with its own custom instruction set, or modify an existing processor design, you need an FPGA to actually see it in action.
* Synthesizers and audio filters. You can do a lot of low latency signal processing compared to even a beefy microcontroller with an FPGA, so if you want to make your own synth sounds in hardware, an FPGA might make sense.
* Computer vision stuff. If you want to make some gadget that does some kind of image processing that is streaming from a camera, and FPGA would work, especially if you wanted it to be small/portable.
* High bandwidth or low latency SDR applications.