If you are in the .net programming world , you might have used free tool .Net Reflector, tool which allows you browse analyze and decompile .net assembly. It can be used to inspect, navigate, search, analyze, and browse the contents of a
.NET component such as an assembly and translates the binary information (IL) to a human-readable form.
Unfortunately this tool no longer available as free tool . Red gate software which maker this tool announced that they will be charging license fee to use this software.You can use the existing version without license fee. If you want to upgrade you have to buy.
If you are .Net Reflector user , still wants free tool to analyze assembly , here are two alternatives. Both products listed below are still beta