If I am correct (of which I'm not 100% sure), commercial apps can be created using WinAsm Studio, but if MA$M (ml.exe, rc.exe, etc.) is used, there might be some issues about having to notice Micro$oft of it (and, perhaps (or certainly) having to pay $$$ to the Redmond, Washington, corp.)
The open-source alternative to this would be to use FASM tools to build commercial apps.
More info on FASM and its license:
What is FASMWelcome