Wireguard really changed the landscape, for me, and my entire approach to networking. Suddenly, VPNs became fast and easy, and where previously impractical for casual (hobbyist) admins, it made creating enterprise-grade secure subnets easy. It's astonishingly stable and reliable, such that my initial concerns about cutting off all access except through the VPN - once a truly nerve-wracking concept - is now a no-brainer. It's made my network administration easier and more secure. My firewalls are simpler.
Wireguard is one of the biggest high-impact, low-visibility networking game changers I've seen in decades.