For data storage, you get 5 MB and for file storage (attachments), 20 MB. To check your developer account, follow the Name | Setup |Administration Setup | Data Management | Storage Usage path.

It offers 5000 API calls every 24 hours.

You can install any number of applications in your developer account.

A 500 MB bandwidth and 10-minute service request time limits (per rolling 24 hours) for Force.com site applications.

You have only two Salesforce full licenses.

You cannot use this developer account for commercial purposes. I would refer to the article at https://login.salesforce.com/help/pdfs/en/salesforce_app_limits_cheatsheet.pdf to check the limits of each edition.