Xpenology isn’t a linux OS like Ubuntu or other common distribution. It’s a bootloader for synologys operating system DSM, which they use on their NAS devices. DSM is running on a custom linux version developed by Synology, so it’s also not real compareable to desktop/server distributions in a direct way. Its optimized for running on a NAS with all of the features they provide.
Sometimes Xpenology is used as a synonym for the full stack of the bootloader and the DSM. It creates the possibility to run DSM on any x86 device like any pc or self-builded NAS. So you can benefit from the powerful multimedia- and cloud-features of DSM without buying a hardware NAS from them.
This will save money and make you more flexible. For example, you can run it on a powerful homeserver, which has much more power than a Synology NAS, so you can also run other things on it (like dev-servers, when you’re a developer).
But its also possible to natively install and run apps on DSM using their package manager. This includes some usefull tools and packages like git, other version-control systems, cms like wordpress, ldap-servers and more. The underlaying OS can be customized, as you can connect over SSH. It should be clear that this should only be done with caution, cause changes on the linux-system could potentically break DSM if you spin on the wrong screws.
And as a person interested using Xpenology you should keep in mind, that his is not a officially Synology release. Although its based on the official Synology DSM which is the same like on a bought hardware NAS from this company. But its not officially supported by them. You could get support from the community for this software, but not from the company itself.
I think this is an important thing because Synology offers really great support. They’re smart using linux and would fix strange bugs remote over ssh. You shoud device if its worth from you to buy a stock-NAS to benefit from them. If you’re a do-it-yourselfer, then Xpenology would be a good and cheap alternative.
Especially for end-users which less or none experience in IT/linux, it would be a better deal for them to buy a Synology NAS, switch it on and have fun without caring about the backend technology.