The CuBox-M measures just 50 x 50 x 50 mm and comes in two variants. The NXP i.MX 8M-based machine supports Android, Linux and can be used for machine learning or natural language processing, among other things. The CuBox-M starts at US$99.
https://www.notebookcheck.net/CuBox-M-A-tiny-mini-PC-that-supports-machine-learning-natural-language-processing-Android-and-Linux.519736.0.html