smali/baksmali is an assembler/disassembler for the dex format used by dalvik, Android's Java VM implementation. The syntax is loosely based on Jasmin's/dedexer's syntax, and supports the full functionality of the dex format (annotations, debug info, line info, etc.)
The primary webpage is http://smali.googlecode.com, and the source is also mirrored at https://github.com/jesusfreke/smali. If you are interested in submitting a patch, feel free to send me a pull request on either site.