From what I've come to understand, JSPM works a lot like NPM, except you can pull packages both from npm and git(hub). We're using it at our startup, and it works quite well. Had to do make a custom build script to make it fit into our Rails application.
Edit: JSPM biggest strength is possibly that it supports a vast set of module loaders (AMD, CommonJS and ES6 modules).
JSPM also normalizes importing in ES6 from AMD, CommonJS, and ES6 (not sure about TypeScript, probably though). It is built on top of System.js, which lets you import modules and allows you to configure the local global namespace.
Edit: Looks like there was a ninja edit since I started typing :)
Edit: JSPM biggest strength is possibly that it supports a vast set of module loaders (AMD, CommonJS and ES6 modules).