Mercurial has a built-in web server which can be used for browsing a repository with a web browser or for allowing remote machines to pull from you. To use it, simply run: 

$ hg serve

And then point your web browser at http://localhost:8000/.

This has most of the features of the full web interface. This server can do multithread/multi-process request since Mercurial version 0.9. If you want to make a more permanent server, you should probably use a [:CGI_Install:CGI-based server].