Found a cross-platform SMIL (Synchronized Multimedia Integration Language) player in AMBULENT.
The AMBULANT Open SMIL Player is an open-source, full SMIL 2.0 media
player. It is intended for researchers and developers who want an
source-code player upon which they can build higher-level systems
solutions for authoring and content integration, or within which they
can add new or extended support for networking and media transport
components. The AMBULANT player may also be used as a complete,
multi-platform media player for applications that do not need support
for closed, proprietary media formats. The player is architected to
support a range of SMIL 2.0 profiles (including desktop and mobile
configurations) and runs under LINUX, Win32 and Macintosh OS X.
Also found a cross-platform SMIL authoring tool: SMILGen, written in Python.
SMILGen is a SMIL (and XML) authoring tool designed to ease the
process of XML content creation. SMILGen understands XML syntax and
handles the nesting and formatting XML. This allows authors to worry
about the content that they are trying to author with out having to
remember each quote and closing brace. SMILGen also understands the
languages it authors, it knows what attributes a specific element
uses or what child elements a given element may contain. Both of
these features help eliminate a number of common XML syntax errors as
well as making it easier to edit with out having a reference to the
language right by your side.