I have a Ruby on Rails web application running on my computer (Ubuntu 10.04) that I'd like to be able to access from a remote machine. My server is mongrel but I have no problem installing another if it helps. How do I set things up so I can access my web application from a remote machine?
Well... if you just want to set it up so that a small handful of people can run through your extremely responsive app while your developing it, then all you need to do is to ensure that the application server is listening on a public-facing IP address (not 127.0.0.1 or localhost). Get your IP address, and slap it in with the port number as a web address.
If you want to serve your application to a larger audience... an intranet, extranet, or over the Internet... then you'll want to start reading up on web application hosting. You'll either need a reverse proxy that load-balances across multiple application servers, or an integrated solution. I would suggest starting with Phusion Passenger to get yourself up and running and then moving on to whatever architecture best suits your needs.