I am not sure it can be called 'very lightweight'. The runtime itself has a large disk footprint, my node_modules is often 100s of MB, and the memory usage is q

I am not sure it can be called 'very lightweight'. The runtime itself has a large disk footprint, my node_modules is often 100s of MB, and the memory usage is quite heavy too (idle Ghost.org blog takes around ~100MB RSS). Some of the APIs are not very portable either, such as fs.watch. Many npm libraries implicitly depend on Linux or OS X. It's convenient though, sure.