WireGuard is a BETA/WIP open-source VPN solution written in C by Jason Donenfeld and others, aiming to fix many of the problems that have plagued other modern server-to-server VPN offerings like IPSec/IKEv2, OpenVPN, or L2TP.
It can be seen as a replacement for OpenVPN although it does not have the versatility, possibilities and track record of OpenVPN.
However, it has two advantages over OpenVPN, it is much faster especially on lower-spec hardware such as Soho routers (my own R7800 goes from 90 Mb/s on OpenVPN to 240 Mb/s with Wireguard) and is easy to setup if you know how, but it is not yet mature and there are sometimes frustrating hiccups.
What makes it so much faster then OpenVPN is not the cryptography, this is more or less the same (use of PKI to calculate/exchange a key with PFS for symmetric encryption). It is the fact that all is done in Kernel space while OpenVPN has to constantly switch between User and Kernel space.
Inherently the executing in Kernel space is less secure, if security is broken than you are compromised big time.
Another disadvantage is that it only supports static routing, so if you use WireGuard to connect to a commercial VPN provider (Mullvad is one of them) they keep track of your IP address. Mullvad implements some NAT'ting and is not tracking your IP address but still it is more insecure then OpenVPN.
Other providers also take measures to counter this problem ( https://www.azirevpn.com/docs/security ) but be sure to look into it.
