(Update: Some of the links dont work anymore because the applications have closed. Take this as an indication that applications for summer internships in Summer 2020 open in May 2019 and close by End June 2019.
GIC (Summer 2020)
Apply via GIC Website:
Ministry of Foreign Affairs Singapore Internship (2020)
The internship, (mini 10 weeks) is between May to September or November to January.
Website Application: March for November internship.
CHangi Airport Group