Five years is long enough to have a release candidate, I think. :)
To avoid conflict with acpiclient (http://sourceforge.net/projects/acpiclient/), which also provides an executable binary named acpi, the acpi binary included with wmacpi is being renamed to wmacpi-cli. Based on the patch from Debian: http://sources.debian.net/src/wmacpi/2.2~rc5%2Bds-1/debian/patches/rename_acpi_to_wmacpi-cli.patch/