MKVToolNix is a set of tools to create, alter and inspect Matroska files under Linux, other Unices and Windows.
Since May 1st 2003, the Matroska libraries themselves and my Matroska tools are officially available. I urge you to download the software, use it and report any errors you encounter to me. I'm always grateful for good bug reports because I make mistakes and you guys normally find them. Your feedback is important to me :)
More Matroska related news can be found in my blog.