The Spark 2 from Positive Grid looks like a miniature old-school amp, but it is, essentially, a computer with some knobs and a speaker. It has Bluetooth, USB-C, and an associated smartphone app.

I found it in Spark 2, an email app from Readdle that has drawn praise from reviewers and users. It is a Mac app, but there are mobile versions for iOS and Android. The company, based in Ukraine ...