Dolphin is an emulator for GameCube and Wii games that has been going for years and still receives regular updates. The latest adds a server browser so that people playing online can host their own server lobbies, both public and private, and search for games to join. Games like Super Smash Bros. Melee, for instance.
This update also adds a new feature called 'Golf Mode' which removes latency for one player at a time, and can be passed to another player when it's their turn. Mario Golf: Toadstool Tour is the example game for this feature, which is particularly finicky about shot timing. Only GameCube controllers are supported by Golf Mode at the moment.
If you're interested in the ethics of emulation, here's our article on the topic.