Where are central government tenders published in India?
On the Central Public Procurement Portal (eprocure.gov.in) for tenders from central ministries, departments and PSUs, and on the Government e-Marketplace (gem.gov.in) for goods and services bought through GeM. Some organisations publish on their own eProcurement instance or only through CPPP's ePublishing module, and Indian Railways uses IREPS.
CPPP is not one list. It aggregates the central GePNIC instances, carries state instances that run on GePNIC, and has a separate ePublishing module for organisations that do not use eProcurement at all. The CPPP Annual Report for 2021-22 puts GePNIC across 31 States and Union Territories and 679 central government organisations.
The practical consequence is that "check CPPP" means checking several listings, and "check GeM" means checking GeM itself rather than the GeM section inside CPPP.