For simple wifi access, a wireless router is all you need. Which you can configure from any web browser. Usually by typing 192.168.0.1 or something close. That information would be provided in your router documentation.
If you're wanting to do more advanced things like having a captive portal, (A login screen once the user connects), then you want a more advanced wireless router. DD-Wrt is good for that kind of thing if your router supports it. DD-Wrt has support for three:
- NoCatSplash: A simple captive portal with a custom landing page.
- ChilliSpot: An open source captive portal client/server, which can support guest usage policies and billing.
- Sputnik: A commercial captive portal client/server similar to ChilliSpot, but backed by subscription fees and a slick, full-featured management interface.