VAXELN is/was a host/target setup for developing distributed realtime VAX applications (ELN = Executive for Local Networks). Hosted on any sensible VAX/VMS system, with targets being a subset of VAX, MicroVAX, VAXstation systems. And a few oddities too (e.g. RTVAX300 VAX-in-a-module, KAV30 RTVAX300-on-VMEbus, rtVAX1000 (KA630-variant in a MicroVAX2 chassis), etc. Obscure targets without publically available VAXELN support (?) include the aforementioned LPS32 and LPS40 VAX-powered printers. The SPD seems to be hard to find online, as does the VAXELN Technical Summary, so what follows is from memory. The usual suspects do seem to have some of the VAXELN docs online in decw$book format. The host and target might be separately licenced. Early VAXELN applications could be written in a multi-threaded variant of PASCAL called EPASCAL. Later, other standard VAX languages were supported too: Ada, C, maybe Fortran, the usual Pascal. Or VAX Macro. The runtime environment was a dedicated RTOS environment, not VMS (e.g. no demand paging) although some VMS-compatible facilities (DECnet, RMS) and routines (some LIB$)were offered. You compiled your application in the usual way, and linked it with VAXELN-specific libraries using the usual linker. The VAXELN system builder was then used to build a bootable system image. A system image would include the hardware-specific kernel and any required VAXELN device drivers. Any optional facilities (VAXELN distributed name service, networking using DECnet and/or TCP, CLI, Xserver, debug) would be combined with any required user applications to make a bootable system image file Booting was supported over the LAN (MOP, maybe bootp), from disk, and in an odd few cases, from ROM. A VAXELN source kit was sold at one stage, though it was far from essential. Pretty much the whole target end was written in PASCAL. In the early days VAXELN had its own threads-aware debugger (hosted on VMS and networked to the target). Once VMS DEBUG got that capability (which came initially with DEC Ada? sometime around VMS V4?) VAXELN targets could be debugged remotely using the standard VMS debugger. Deep joy. Iirc, VAXELN V4.3 or thereabouts used to be on CD in the 1990s (1993?). There were a couple more versions after that, but no huge changes I can remember. When Alpha came along, VAXELN was left behind. DEC worked with Wind River to get a version of VxWorks for Alpha (VxWorks was an "industry standard" RTOS, somewhat different in concept to VAXELN). Both claimed to have POSIX compatibility for the RT stuff. A thin VAXELN veneer was added on top of VxWorks for those who might be interested. The product became part of DEC's Embedded+Realtime Group, which was sold off to SMART Modular Technologies, in the late 1990s (?), and the product subsequently vanished. I haven't recently been able to establish the product's current status, though I didn't try real hard. It was a great RTOS if you wanted to think more about the application design and less about the intricacies of device drivers and networking and other such traditional RTOS trivia. I'm told its concepts mapped nicely onto the "channels and pools" from "Communicating Sequential Processes". Be interesting to know what lies behind the original enquiry from LinkedIn. I may be able to offer more info if necessary. It might not be quick, and the formatting may be messed up again (sorry). Hope this helps, regards John