At the moment the only available ones I know of are the Aries (not Mini) which is expensive and the Squeezebox stuff, which is not currently produced but has a second hand market.
Once Roon 1.2 is released (with RoonBridge, formerly RoonSpeakers) then there will be many more options. A CuBox-i running a minimal Linux with a Wi-Fi dongle and a linear power supply or battery would be an inexpensive option. I’d really want to find out if that worked well enough before getting any fancier.
Edit: Nearly forgot the Chromecast Audio which is on the roadmap to be supported as an endpoint. It won’t do DSD though.