What has ISRO done?
In one go, Indian Space Research Organisation (ISRO) launched 20 satellites. They include two student satellites from Indian universities and 17 of four foreign countries.

A PSLV C-34 rocket lifted from the Satish Dhawan Space Centre, and placed a Cartosat-2 Series satellite about 505 km above the Earth's orbit. 

About Cartosat-2
The 725.5 kg Cartosat-2 would be used for Earth observation. According to ISRO, the imagery sent by the satellite will be useful for cartographic applications, urban and rural applications, coastal land use and regulation and utility management like road networking.

Past missions involving multiple launch
It may be recalled that ISRO, in 2008, launched 10 satellites in a single rocket. In 2008, PSLV-C9 launched a Remote Sensing satellite CARTOSAT-2A along with Indian Mini Satellite (IMS-1) and eight nanosatellites.
In 2014, Russia launched 37 satellites in a single mission.