Consider the following:

1. Aarogya Setu

2. CoWIN

3. DigiLocker

4. DIKSHA

Which of the above are built on top of open-source digital platforms ?

The correct option is 1, 2, 3 and 4.

All four digital platforms listed are built on top of open-source digital platforms or have open-source components:
1. Aarogya Setu: The government of India released the source code of the Aarogya Setu contact-tracing application on GitHub, making it open-source.
2. CoWIN: The platform used for Covid-19 vaccination registration and tracking was built as a digital public good, with plans to make its technology open-source for global adoption.
3. DigiLocker: DigiLocker is built using open-source technologies, APIs, and frameworks (such as LAMP stack, PHP, and other open standards).
4. DIKSHA: Digital Infrastructure for Knowledge Sharing (DIKSHA) is built on top of Sunbird, which is an open-source digital infrastructure platform designed for learning and education.