Another common use case is real time video stream manipulation. There is a demo by Bunnie Huang who uses an fpga to intercept, decode, then reencode HDMI video streams (including microsecond timing manipulation of one of the data lines) in order to do video overlays on the video (for things like captions).
In general the main use cases are really for things that require lots of parallel and/or low latency processing.
Two examples that I have been loosely involved with; * Google's CFU playground which is all about profiling and adding small number of new OpCodes to build an accelerator for a specific ML model (http://cfu-playground.rtfd.io/). * The Fomu workshop (https://workshop.fomu.im) which walks though treating an FPGA like an embedded MCU where you can then modify the MCU!
What are the best hobbyist use cases for FPGAs? Most of the stuff I do can be accomplished with microcontrollers or embedded systems like RPi, I imagine FPGAs become more important when you're doing things like DSP or hard realtime requirements, which don't come up super often in hobbyist projects.
I'd like to do more hobby projects involving FPGAs so what sorts of things might low cost FPGAs be useful for in that realm?
I'm thinking of building a clock that integrates a local atomic oscillator, outputs from an embedded system running ntpd, and drives a local VFD as a sort of orientation project.