INVedit is the (more like “some kind of”) successor of NBTedit. With it you can create your own porta- wait, wrong game. You can use it to edit your inventory both Singleplayer and Multiplayer, if you’re the server host.
INVedit usually is forward-compatible with new versions of Minecraft, new items will just be missing.
You will need the .NET Framework 4.0 (Client Profile) to run this ? you usually have this already installed. May also work with Mono or Wine on Linux and Mac, but there is no guarantee or support. If you’re an unexperienced Mac or Ubuntu user, this is probably not the right tool for you. There are a few unofficial tutorials on how to do it, but I really suggest using a different tool or mod.