On Thursday, Google will announce their OpenSocial platform—an open API for social networks. Clearly a shot at challenging Facebook. I still have little interest in building apps on top of social networks, but the APIs for profile information and social graph will be very interesting.

I received an invitation to the Google Mashup Editor a couple of days ago. I haven’t had time to really play with it yet, but I wanted to give my initial impressions.

When I first heard about it, I was under the impression it would be similar to Yahoo Pipes. While the idea is similar — primarily, using feeds as data input for building web apps — the implementation is completely different. Where Yahoo Pipes is a visual app builder, Google Mashup Editor is a web-based IDE. It consists of a text editor, feed viewer, and a test environment.

The real meat of GME is the <gm:> tags. You can think of this as a templating language. The tags provide UI controls, data access, control structures, etc. You combine these with basic (X)HTML, CSS, and JavaScript to build your mashup. When you run the application, the tags are “compiled” into standard JavaScript.

Now, here’s the $60,000 question: If the <gm:> tags are simply template tags that turn into JS, why didn’t Google just release it as a library? It seems like it would be simpler — and more useful — to let people download a Google Mashup Library than to build an entire IDE around it and restrict applications to only living on their servers. But maybe that’s coming later.

As I said, I haven’t had much time to play with it yet, but hopefully I will get something built with it soon to really test out what it can do.