Lars Brinkhoff made an implementation of the supdup protocol available. It includes a curses client and server.

Brad Parker ported an old BSD Chaonet driver to Linux. From the README:

Chaosnet was an early networking protocol developed at MIT.  Near as I
can tell it was developed before TCP/IP, perhaps during the early
Arpanet NCP protocol days.  The protocol was supported by Symbolics
lisp machines as a native networking protocol.  Older machines (like
my ancient 3600) don't have TCP/IP support but do support Chaosnet on
Ethernet.  This is a port of some really really old BSD kernel code
to modern day linux.

I doubt anyone would want this code unless they have some old lisp
machines they are playing with...

I've tested this code with General 7.2 and 8.3.  It allows QFILE
transfers back and forth, which was my goal.  I also hacked the RTAPE
server code to do RTAPE support using a disk file instead of a real
file.  This is useful for archiving...

-brad

Just what I was looking for to make some backups.

Finally a workable checkpointing solution for all Linux processes!

Checkpointing is the technique of storing a running process's state in such a way that a process can be restarted from the point at which the checkpointing took place. UCLiK is a checkpointing system for Linux. It was designed as a kernel module, and thus requires no modifications to the running kernel's code. UCLiK provides transparent and flexible checkpointing support to the Linux kernel. The ultimate goal is for UCLiK to be able to checkpoint Any Process at Any Point in time.

It's not orthogonal persistence like in EROS, but probably Good Enough (tm) for most applications.