NSE NOW, Nest Trader and Sharekhan have RTD link in excel.
Other's might also have, but I don't know.
In Excel, it do it this way:
1. Create a market watch with a list of scrips that you want to scan for gap movements. Market watch must have previous close and open values.
2. Via RTD link, send the data to Microsoft Excel.
3. Add an additional column in Excel where you calculate
Gap% = [(Open-Prev. Close)/Prev. Close]*100
The gap ups will be positve and gap down will be negative.
4. Format it as a table.
5. Just sort the table based on your above created column from high to low.
On top of list will be top gap ups, on bottom of list will be top gap downs.