I've been writing a REST API-based service and testing on a Developer Edition org user and it's been working fine, but it stops working for a Salesforce user with a Group Edition org. I get this error:
API_DISABLED_FOR_ORG: The REST API is not enabled for this Organization.
Which API will work on the most number of org editions, including a Group Edition?
There must be some API that does this because Yesware seems to be doing it. I have a Group Edition account and hooked up Yesware without installing their app on Salesforce and they are able to create Tasks for existing Accounts.
Note that I am not looking to release an app in AppExchange (no Apex code). I only want to OAuth a user and then create/update records to their Salesforce account.