Built by cloud development agency FirmCloud in collaboration with FreshBooks, the FreshBooks Connector for Salesforce allows an enterprise to smoothly create an invoice for a contact or opportunity within their CRM.
Before the integration was announced, hundreds of Salesforce CRM customers had requested that some bright AppExchange developer take advantage of the FreshBooks APIs. Despite the popularity of Salesforce.com, FreshBooks had first been connected to four other CRM systems.
In terms of functionality, it looks like converting contacts and opportunities in Salesforce.com to invoices is fairly easy. In addition to simply moving data from one platform to the other, the Connector creates a tab within your CRM to monitor activities on your 20 most recent invoices. There's a 15-day free trial for the app, but after that it'll cost you $50/month per organization.
Overall, this new app is a match made in heaven, for sales at least. If you're seeking to try it out however, you'll have to get it direct from FirmCloud, since it's strangely hidden as a private feature in the AppExchange.