The COM Based Technology is used to develop Components that are managed and can be interoperable with various Dot Net Languages.
COM Based Technologies are COM, COM+, ATL.
We can even build Dot Net Components as of now.
COM Based technology helps build components of any kind, for eg. Business Logic Components, Data Access Components and even UI Components.
Windows Operating System has many components shipped along with and can be used by applications.
COM Components can be used by Dot Net Applications and are also managed by the CLR by creating Runtime Callable Wrapper objects.
COM+ has Component Services utility to manage them.
COM has a short learning curve and can be easily learned if read from Right Books.
Designing Component-Based Applications
Inside Distributed COM
.Net and Com: The Complete Interoperability Guide