“Network Link Conditioner” essentially does the opposite but it’s a really neat tool: it lets you degrade your connection, so you can test how software reacts to degraded network conditions, and don’t need to install and configure third-party proxies and the like.

The biggest drawback is it affects the entire machine, you can’t enable the conditioner on a per-process basis, so it can be a bit rough on the other “normal” usage of the machine.

There’s also a version on iOS.