The amazing Salesforce platform allows us to create public website even with developer edition of the platform. The website address will be either SubDomainPrefix.force.com or www.YourCustomDomain.com. This is my public website created using Developer Edition. The major limitation I found for a force.com public website is the 500MB of daily bandwidth and ability of creating only one website.
Reference: An Intro to force.com + steps for creating your own website in a few minutes, Force.com sites overview – contains more details about possible custom domain options, Force.com Public Website implementation guide