I needed a quick way to test a few things on a webapp running locally (on my Linux box) from another machine running Mac OSX.

Quick and easy way (although insecure, make sure you only do this on a private LAN) was to use socat.

Install on Archlinux (server):

sudo pacman -S socat

Install on the MacOSX client via homebrew:

brew install socat

Proxy local connection to the LAN (on the server; assuming the webapp runs locally on port 5000):

socat tcp-listen:8000,fork tcp:localhost:5000

Proxy remote connection to localhost (so we can access it with the benefits of "local" apps in a browser; otherwise, we would have to have the app served via HTTPS to, eg. use location services):

socat tcp-listen:5000,fork,bind= tcp:192.168.x.x:8000

..where, of course, 192.168.x.x is the IP of the server machine.

Now, you can just visit http://localhost:5000 from the client.