Open source Hercules is still alive. Attempts to commercialise it (TurboHercules) ran into legal trouble with IBM, but to my knowledge the open source Hercules project hasn't faced any issues. (Disclaimer: I'm not a lawyer, I don't work for IBM, etc.)
IBM's licensing agreements don't allow you to run current versions of its mainframe OSes under Hercules. IBM will sell you an equivalent technology which you can legally run their OSes under, an x86 mainframe emulator called zPDT, but it is quite expensive (I have heard figures quoted like USD 5000). This is where TurboHercules ran into problems–they wanted to run current IBM OS versions under Hercules, but IBM says that violates their license agreements. TurboHercules tried to get the EU to force IBM into licensing their OSes to run on Hercules, but they didn't succeed.
By contrast, you are legally allowed to run old versions, 1970s vintage–in those days, IBM chose to release its operating systems into the public domain. That has little practical use, so can't be commercialised, but lots of people do that as a hobby, and there is stuff happening in that scene. I recommend this distribution of MVS 3.8J if you want some basic exposure to MVS – http://wotho.ethz.ch/tk4-/ – a lot of the basics, like JCL and TSO, aren't hugely different, although a lot of features you'd expect on a modern z/OS system (e.g. ISPF, Unix, Java, TCP/IP, peer-to-peer SNA) are missing in this circa 1981 system.
It is also perfectly legal to run Linux under Hercules. I never have because it seems somewhat pointless–the differences between z/Linux and x64 Linux are minor–but I can see practical uses – you can port a project/product to z/Linux so your customers can run it on their IBM mainframes without you needing an IBM mainframe yourself.
> it is quite expensive (I have heard figures quoted like USD 5000).
A bit of correction, I'm afraid. That's the cost for mid-shelf copy of Visual Studio 2009 or so. It's not expensive at all for corporate purposes at any company I've worked at. Top-shelf Visual Studio was set for 10,000 for a long time (some checking of current costs suggests they've redone their pricing model).
Expensive software for functioning companies, broadly, might be north of $100K. I can't speak to specifics, of course.
It's quite a reorientation of what "expensive" means when you get involved, even a bit, in corporate purchasing and negotiation.
Expensive for whom? Yes, for a large corporation USD 5,000 is easily affordable.
But consider someone like myself. My job isn't focused on mainframes. I very rarely have had anything to do with them at work. Even though my employer could easily afford USD 5,000 to buy me a zPDT if there was a business case for doing so, they won't because there isn't really one–in the last five years, I've only once had to help a customer with mainframe integration issues, and we used a partner company with mainframe specialists to handle that engagement for us. However, I'd still like to learn the technology. I'm not sure I'd ever really want a job in it, but it fascinates me. But I'm not forking out thousands of dollars of my own money just so I can play with z/OS or z/VM.
I think this is a problem with mainframes–even if someone is interested in the technology, it is very hard to learn about it unless your employer uses them (and in a large company, even if your employer does, your own job might still have little or nothing to do with them.) I would have thought IBM would be more keen on spreading knowledge of its own technologies around–it might actually make it easier to sell them to people–but it doesn't seem to be on IBM's radar. HP has the hobbyist program for OpenVMS, IBM could set up a similar program for mainframes (and IBM i too), but that has never happened. (I have heard some folks have tried to talk IBM into it, but they have never got anywhere.)
I totally agree that this is a problem for the mainframe, and I personally have tried to talk to IBM about this (and obviously haven't gotten anywhere). This is a huge missed opportunity for them. I regularly encounter folks that would like to learn the platform, even at a hobbyist level, but it's simply not accessible.
FWIW... I know it's not exactly what you're looking for, but IBM does host a Master the Mainframe contest each year. It provides free access to current z/OS systems for a while (few months, I think) and a project consisting of a series of challenges that guide you though learning the environment. IIRC... you must be an enrolled student to actually win the prizes, but anyone can sign up and perform the activities. One of the mods on /r/mainframe helps coordinate the contest if you're interested in learning more about it.
Kudos to those intrepid enthusiasts who implemented it and kept it going all these years. It's sad that they weren't able to capitalize on their efforts, but as a F/OSS supporter, I thank them for giving us at least the potential to play with mainframe technology (without running mainframe-compatible hardware).
Fun thought: I wonder what it would take to layer Hercules directly over ESX/i to create a poor person's "mainframe VM"? I mean, besides installing Hercules on a Linux guest on ESX/i.
IBM's licensing agreements don't allow you to run current versions of its mainframe OSes under Hercules. IBM will sell you an equivalent technology which you can legally run their OSes under, an x86 mainframe emulator called zPDT, but it is quite expensive (I have heard figures quoted like USD 5000). This is where TurboHercules ran into problems–they wanted to run current IBM OS versions under Hercules, but IBM says that violates their license agreements. TurboHercules tried to get the EU to force IBM into licensing their OSes to run on Hercules, but they didn't succeed.
By contrast, you are legally allowed to run old versions, 1970s vintage–in those days, IBM chose to release its operating systems into the public domain. That has little practical use, so can't be commercialised, but lots of people do that as a hobby, and there is stuff happening in that scene. I recommend this distribution of MVS 3.8J if you want some basic exposure to MVS – http://wotho.ethz.ch/tk4-/ – a lot of the basics, like JCL and TSO, aren't hugely different, although a lot of features you'd expect on a modern z/OS system (e.g. ISPF, Unix, Java, TCP/IP, peer-to-peer SNA) are missing in this circa 1981 system.
It is also perfectly legal to run Linux under Hercules. I never have because it seems somewhat pointless–the differences between z/Linux and x64 Linux are minor–but I can see practical uses – you can port a project/product to z/Linux so your customers can run it on their IBM mainframes without you needing an IBM mainframe yourself.