Open source Twitter client

As some of you will know, I am quite a heavy user of Twitter. I've been hunting for a little while now for an open source Twitter client for OS X.

I've found a couple of free apps e.g. Twitterific, which in all fairness is a very good client, but not open source, which is what I'm looking for.
Now, there is one client that is open source in one sense, called spaz. The problem I have with this is that it's built on Adobe's AIR technology, which is not open source. I had an interesting discussion with the developer of spaz where he mentioned technologies like Java (although that is now going open source) and asked me if apps built on layers like that were not 'true' open source.
This is an interesting question and one that I'd like to explore further. Does a piece of software have to be open source all the way down the stack for it to be truly open?
The major problem with this from my context is that I'm running OS X, which, although built on some open source is not an open source operating system by any stretch of the imagination.
I'd very much like to get some reader thoughts on these points and I'll probably be doing a longer post on these issues in the future.

In the mean time, if anyone finds an open source Twitter client not built on AIR then please let me know.