Stein - Use Google Sheets as your no-setup database
UProc for Sheets - Boost your sales, marketing and IT tasks from Google Sheets
Sheetson - Instantly turn any Google Sheet into RESTful API
Sheetlist - Discover free Google Sheets for marketing, finance and more
Sheetsu - Turn Google Spreadsheet into API
Mattermark in Salesforce AppExchange - Automatically enrich leads in Salesforce with Mattermark