ApiChange does take a set of "old" assemblies and a set of "new" assemblies which are diffed for potentially breaking Api changes:
ApiChange -diff -old HelloWorldV1.dll -new HelloWorldV2.dll
LibCheck allows you to compare two versions of an assembly and determine the differences. The tool reports the differences as a combination of "removed" and "added" APIs:
LibCheck -store HelloWorld.dll 1.0 -full C:\HelloWorldV1\
LibCheck -store HelloWorld.dll 2.0 -full C:\HelloWorldV2\
LibCheck -compare 1.0 2.0
See also "Working with LibCheck", "Highlight Public API Differences Between Assembly Revisions" and "Api Diff Between Assemblies" articles.
