bzip2 is a freely available, patent free (see below), high-quality data compressor. It typically compresses files to within 10% to 15% of the best available techniques (the PPM family of statistical compressors), whilst being around twice as fast at compression and six times faster at decompression. 

http://sources.redhat.com/bzip2/

There are Tcl bindings available for it [bztcl] (except they are LGPL) . It would be a great addition to have a Tcl VFS backend available.

[Vince] -- writing a tcl-vfs backend for bztcl shouldn't be difficult.  Just copy the .zip (zipvfs.tcl) or .tar (tarvfs.tcl) backend and make the relevant changes.  It's all pure Tcl,....

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[LES]: There must be some mistake above. While bzip2 is indeed the strongest compression format and produces the smallest files, I've also found it to be one of the slowest formats. It's usually twice as *slow* as other formats, not twice as fast.

[DLR] It refers to twice as fast as PPM compresors (reference ones). For day to day usage I find the difference in speed negligible compared to the substancial savings in space (relative to gzip compression)

[LES]: Hard drives get cheaper and space more abundant every month. Time has only become scarcer ever since I was born.