Traditionally, compilers were built as tools for end-user developers. LLVM , instead, is a library you can use to make a compiler. Clang, for example, uses the LLVM API to produce a form that the LLVM subsystems can compile into actual machine code.

Interesting, clang actually did this too - it itself is a C/ObjC/C++ parser library, which can be used to make a tool.

LLVM is fantastic because, as a language developer, you can focus on your parsing and language-specific features without needing to concern yourself with machine code generation. LLVM does that all for you.