A facility for developing what offline? Developing a component that caches Salesforce.com data offline? Or literally developing a Force.com app offline?
For the former, Salesforce.com offers a product called Offline Edition. For the latter, no.
The Force.com IDE offers an offline mode, where you can edit source code without being connected to the Force.com servers. But you can't execute Apex or display Visualforce pages offline--the server platform is the only runtime environment for these features.
For the former, Salesforce.com offers a product called Offline Edition. For the latter, no.