Used by many VPN clients (apps and routers alike) underhood, it has been the standard for many years as the de facto protocol for VPN, an alternative that is promising faster speeds and better performance but is currently new is WireGuard.

This piece of software is the least user-friendly one you can get for Windows platform. Unless you are majored in computer science you will 100% fail to make it work. The so called "manuals" are basicly a specifications, list of features without any step by step instruction of how to make it work. It seems that this extreme un-userfriendliness and the links to the product are hidden from their website is done on purpose, to push everyone to buy their uncompetitive commercial version of the product (which also requires your CVV code before you even install the product, which is at least suspicious)

save your time and ignore OpenVPN

The application is declared open source, and there are even repositories on github and gitlab. But neither there nor there is it possible to leave bug reports or wishes for the development of the application, just as compiled binaries are not provided. In addition, the application does not support working with the wireguard protocol, that is, it is useless for me.

The software is great, and the UI is pleasant. When a VPN provider gives you their own crappy client, you can just use this one instead.

The only downside is that it doesn't have a kill-switch. I mean it technically does, but it doesn't work in practice.

It is installed on all mobile devices - laptops, and Android and iOS-phones. One click, and I can have in any public wifi network a secure tunnel to my homenetwork, thereby surfing the net protected by my firewall and kept ad-free by PiHole.

It takes creating an online profile to use it - this makes the whole idea of anonymization obsolete

It's open source. It's cross platform and it's easy to use/configure