How would you classify the following type of online interactions? Explain in one sentence:

a$.$ An online hotel reservation platform that allows users to book hotel accommodation at many localities as per user's requirement

b$.$ A company's website that lists information of blood donors within a given locality

c$.$ A website that allows the user to pay for the recharge for any mobile

d$.$ A company that allows the user to book a gas cylinder online

e$.$ A company that allows the user to buy an insurance policy from any service provider

f$.$ A website that allows registered users to listen to music