An XSL formatter developed by Sun Microsystems is being donated by Sun to open source. This paper presents the rationales for developing an XSL formatter and for making it open source. It also describes the formatter's architecture, highlighting trade-offs made because of the decision to make it open source, because of compatibility with other open source efforts, because of internationalization requirements, and because of the requirements of the XSL Recommendation. This paper also discusses the future direction for the formatter and how you can become involved.