ArcFS

ArcFS is an archiver for RISC OS, claimed to have similar functions to Spark and to have a free read-only (de-archiver) version, so that you don't have to buy anything to open archives created in the ArcFS format.

The (rather over-used) .arc file extension is used, even though the format is not compatible with the various other formats for various other platforms that have also used this extension.

Links

 * Page in riskos.info site
 * Page in ARM Club site