None of the above, it is not made for computation intensive tasks (it would be extremely inefficient and expensive). You can make crypto kitties though.

current version of Golem is only focused on rendering in Blender and LuxRender.

https://github.com/golemfactory/golem/wiki/Roadmap

many classes of transactions and economic activities that require the facilitation of real-world middlemen (drafting & enforcing contracts, coordinating buyers & sellers, etc) can be turned into something that exists entirely on the network and automated. a straightforward example is a gambling pool that exist purely in software, on no particular device.

vue.js is just for a pretty frontend for the apps.

Is there a reasonably simple (and reasonably documented) yet reasonably usable free open-source application of this kind available to study?

By the way, can I use the blockchain as a decentralized replacement for a database (e.g. instead of MongoDB/CouchDB) for my app so that all the data submitted (provided it's lightweight immutable semantic data, i.e. "facts" accompanied with small (never bigger than 256 symbols, usually smaller) amounts of parameters) will be stored in the blockchain? If yes, where do I get started (without having any blockchain experience to the moment)? Is there some kind of tutorial that would explain this vue-ethereum-ipfs things (the README.md of the repo by the links makes near-zero sense to me but I am eager to develop a "multiplayer" VUE app that would store its data "nowhere and everywhere")?

you could take a look at openbazaar, which (as far as i know) is the leading decentralized market software currently being developed. it uses cryptocurrency for payments and ipfs as a filesystem.

you surely could use the blockchain as a database, because you can attach small amounts of arbitrary data to blocks[1], but it would be very inefficient (transaction fees!). something like ipfs is probably a better solution.

i'm not a software developer, i just think this stuff is really cool and follow projects. someone with more technical chops could definitely give you some better pointers! i do have this bookmarked, though: https://dappsforbeginners.wordpress.com/

[1] https://poex.io/about

CryptoKitties and Etherdelta.