Now there's a blast from the past! I'm the "13-year-old 8th grade son" in the testimonials!
Hercules is pretty neat, and, for a very portable pure emulator, is reasonably quick as well. I definitely recommend giving MVS 3.8j a spin since it's readily (and legally) available.
Mainframer here. Hercules is a pretty amazing piece of software. (Fun fact: One of the main developers, Jay Maynard [1], is also known as the "Tron guy") Unfortunately, Hercules is as close as the average person can get to the platform without working for a corporation that runs z/OS (the modern successor to MVS) or Linux for System z (s390x Linux running on mainframe hardware) in their shop.
The platform has a big image problem. I personally blame IBM for not maintaining relationships with their education customers in the early 80s. The high cost of the hardware drove universities to adopt the new and exciting (ie cheaper) distributed platforms, and thus breeding a generation of distributed-minded graduates never even hearing about the mainframe platform except in history books. I know, because I was one of them.
Now the industry is now facing an exodous of their mainframe experts as most near retirment. The average age is something like 55-60, ready to retire [2]. There just isn't any young, talented mainframers being educated. IBM has realized this, and they've started the "IBM Academic Initative" to partner with schools and incorporate mainframe into their curriculum. It's a start, but the damage is done.
The technology, however, is top notch. The closed-source software/hardware model provides a lot of performance gains over the open source model. z/OS is updated every year and IBM releases new, faster hardware every year. And it's not always more expensive. An EC10 can consolidate several racks of Linux blades into its zVM hypervisor (btw IBM has been doing virtualization for 30+ years) while processing 145,000 credit card transactions per second into a single refrigerator-size machine 24x7x365.
If you are looking for a new career, consider mainframe [3]. It's the backbone of financial, retail and data processing industries. It may not be as glamorous, but it's not going anywhere. And when all that old mainframe talent retires, you can write your own check.
The IBM System z Remote Development Programs (zRDP) [1] costs a little less than $600 per month, and gives you access to a system sufficiently robust for learning. I don't know how it would work to have multiple IDs for multiple people on the same subscription. But if you can trust everyone in a group of 10-20, and work out a shared access schedule, then it can be quite affordable. You might need to come up with some development project as a stated reason to join, but that is easy enough.
It sounds like if IBM were serious about getting people skilled up on their platform you'd be able to get access to a system for a bit less than $600/month. $0/month sounds about what they should be shooting for.
The university I studied at was sponsored by Sun, before they were bought by Oracle. Oracle no longer had any desire to support universities. So the university looked around and IBM gladly picked up where Sun left: They donated (or sold for a low price) a mainframe to the university. Students now can play on the mainframe.
As someone who has spent a few years with zLinux, the "several racks of blades with zero downtime" is a story, but it's not always reality, shall we say. Good platforms, but you need to scrutinise the price:performance quite carefully.
Nationwide is the poster child of consolidating on zLinux. [1] But of course, that's all marketing from IBM. I believe their target market is to customers who already have the z hardware being used for their z/OS processing. The infrastructure is already there, then customers just pay for the increasing in IFLs.
The killer feature is I/O and proximity to mainframe data. With hipersockets, you get memory-to-memory speed networking to your mainframe data. You just can't replicate that in VMware.
z/VM, z/Linux (bare metal or under VM), z/VSE, z/OS, and I believe z/TPF. That's the newest stuff. It will also emulate 360's. I think the first thing I ever ran on Hercules was OS/360 MFT! Anyone can legally run VM/370 and MVS 3.8(?) and anything older. Oh ya, MTS, Music/SP, etc. too.
Hercules is pretty neat, and, for a very portable pure emulator, is reasonably quick as well. I definitely recommend giving MVS 3.8j a spin since it's readily (and legally) available.