We spent yesterday at Salesforce&'s first ever hackathon, called Cloudstock, which aimed to spur innovative uses of cloud-based APIs. Developers were given a choice of over 20 different platforms they could build off of including' Force.com, Twilio, LinkedIn, Amazon Web Services, Google, and more.

Hacks ranged from an image resizing tool for Salesforce apps to an SMS-based contact manager to a mashup of LinkedIn contacts with Yahoo job listings. We even caught a Twilio-based SMS game that conference attendees played during intermission.

Out of over 30 applications, judges chose five startups to highlight and here are the winners:

Best in Show: Tic Tac Toe using Twilio API.

Best Enterprise Application: Salesforce to eBay listing app.

Best Mobile Application: Geo address book. Created by Andrew Mager and Chris Hutchins of Simple Geo, the app allows you to search your LinkedIn and Salesforce contacts by your location.

Best Commercial Application: Event reminder app Boomerang.