You're right, it's not natively on Linux, and you wouldn't use it on Linux today since the kernel supports lower latency IO and has better scheduling. Jack has gotten so much better. We didn't have that at the time and I was desperate to use the only interface card I had.
That said, there are plenty of open source implementations of ASIO drivers now that aren't hardware tied.
> you wouldn't use it on Linux today since the kernel supports lower latency IO
Actually you absolutely would use it, in the same way you did back then.
WineASIO is a layer that allows a Wine application to use the ASIO API. Since ASIO is not a part of Windows itself, anything that wants to use ASIO can't do so on "bare Wine", and Wine doesn't allow for the installation of a windows kernel driver layer like ASIO. Hence: WineASIO - an implementation of ASIO for use by Windows applications running inside Wine.
Also, Ubuntu 14 dates to 2014; JACK dates back to 2002. Very little, if anything has changed about JACK since 2014. AFAIR, WineASIO could or did use JACK itself at some point in its development history, since it was a pretty natural fit.
I don't know of any open source ASIO implementations. The only 3rd party one of, ASIO4ALL, is not open source. Then again, I don't track the Windows environment much at all.
Checkmate ;) j/k
You're right, it's not natively on Linux, and you wouldn't use it on Linux today since the kernel supports lower latency IO and has better scheduling. Jack has gotten so much better. We didn't have that at the time and I was desperate to use the only interface card I had.
That said, there are plenty of open source implementations of ASIO drivers now that aren't hardware tied.