No, it is direct peer to peer. Thus both computers need to be connected at the same time. If you want async you need a third computer to store the data.

It is a really elegant and ergonomic way to transfer files between computers. It doesn't need any preparatory setup like launching a "server", as with ssh or http. A single, short command line on each computer, and the file is copied.

The only pre-requisite is that both computers are actually connected to the internet. Unfortunately, NAT and other shit broke the internet so this is a difficult pre-requisite to fulfill nowadays. A sad tragedy of our times.

It still often works to transfer files directly between computers in the same lab.

   dest$ nc -l  > file

   src$ nc $IP_DEST < file

On some installs of netcat you'll need to specify a port because they don't have a default one (typically 31337). Look at the manpage to see what is the case for yours.

clearly someone needs to make natcat