It's more like a Synology OS for home made NAS.

It also does containers and VMs, but started as NAS software.

boosacnoodle: Haven't really heard about unraid before. It looks like it's just an expensive Portainer view?

Just a good, easy to use home NAS distribution. Been running it for years now. Bring a computer and a bunch of hard drives, install UnRaid and suddenly you've got something very similar to a Synology (better IMHO).

The best feature of unRAID IMO, is the ability to mix and match drives.   Have some 2tb, 4tb, 8tb, 16tb whatever.  You parity drive (the drive used incase of a failure) needs to be as big as your biggest drive, but he rest can be anything, and it will make all space avaialble.

Other NAS systems it will make each HDD use as much space as the smallest drive.  

Also the data is completely written to one drive, so if the 2 drives die and you lose the parity, you can just read the complete files off the individual drives on another computer.  normal NAS the files are split up and this is impossible.  this does have some draw backs, but in a home setting, its great.  Ive used it several times.

It's also handy from an upgrade perspective too. Upgrade your Parity to a bigger drive then you can upgrade the rest. I did this years ago with upgrading from 4tb drives to 8tb drives.

So just triple checking - the lifetime $129 is still on their website, if I buy this today I'm assuming it will be grandfathered right? I read the linked pricing change page but it doesn't say when the change is going to be implemented.

Also, how hard/easy is it to set this up on an old HP microserver (one of those with iLo) currently running windows 10 and RAID0? 

yes, everyone will be grandfathered in up until they change their pricing.  theyve been quite open about this.  which is great of them.

Download a trial, install to USB and see if you can boot into it and see your drives.  but i dont think it should be a problem.