With Google Apps Script you can:
Automate repetitive processes and workflows. Create scripts to automate expense approvals, time-sheet tracking, ticket management, order fulfillment, and much more.
Link Google products with third party services. A script can send custom emails and a calendar invitation to a list from a MySQL database.
Create custom spreadsheet functions. Apply customized formatting or do complex analysis on data in Google Spreadsheets.
Build rich graphical user interfaces and menus. With Google Apps Script, a company could power an internal application for purchasing office supplies, where users could shop via a customized menu interface