This project really showcases the power of open source and passionate people building something for the sheer joy of it :)
It's basically an EP32 chip with a tiny smidge of custom hardware that's been programmed to speak the serial protocol of quite a number of 8 bit machines.
I have one for my 800XL and that speaks Atari's SIO protocol.
The depth and breadth of software for the thing is amazing, and overall I find the whole project incredibly inspirational.
Lately, they've been on a kick of creating a project where they've instrumented classic Atari games to post high scores on the internet, with a website 'lobby' where you can sign up to play games online with others.
Totally love mine, and which I had a bigger house so I could have an Apple II and a C64 and get the Fujinet for those platforms as well :)
No problem! You don't need to own the hardware. You can use the pre-built fujinet-pc if your platform is supported, or just run Altirra (works fine from WINE if you're not on Windows) and install the fujinet SIO adapter.
It's pretty cool stuff getting on the internet with an emulated atari running an emulated fujinet IMO :)