Gentoo recently made the switch from lzma-utils to xz-utils, to quote the project page at http://tukaani.org/lzma/:
LZMA Utils are legacy data compression software with high compression ratio. LZMA Utils are no longer developed, although critical bugs may be fixed as long as fixing them doesn't require huge changes to the code.
Users of LZMA Utils should move to XZ Utils. XZ Utils support the legacy .lzma format used by LZMA Utils, and can also emulate the command line tools of LZMA Utils. This should make transition from LZMA Utils to XZ Utils relatively easy.
As you are probably aware, Portage has largely used lzma for the past year - before which bzip2 was the compression standard of choice. If alarm bells went off in your head when you saw this message:
[blocks B ] app-arch/lzma-utils ("app-arch/lzma-utils" is blocking app-arch/xz-utils-4.999.9_beta)
You can rest easy uninstalling lzma, the xz-utils package comes in a good ol' fashioned tarball and it works as a drop-in replacement for it so it's safe to unmerge lzma-utils completely then - before emerging anything else - emerge xz-utils:
# emerge --unmerge lzma-utils; emerge xz-utils app-arch/lzma-utils selected: 4.32.7 protected: none omitted: none >>> 'Selected' packages are slated for removal. >>> 'Protected' and 'omitted' packages will not be removed. >>> Waiting 5 seconds before starting... >>> (Control-C to abort)... >>> Unmerging in: 5 4 3 2 1 >>> Unmerging app-arch/lzma-utils-4.32.7... * GNU info directory index is up-to-date. Calculating dependencies... done! # emerge xz-utils Calculating dependencies... done! >>> Verifying ebuild manifests >>> Emerging (1 of 1) app-arch/xz-utils-4.999.9_beta >>> Downloading 'http://gentoo.osuosl.org/distfiles/xz-4.999.9beta.tar.gz'
I'll take this opportunity to point out that in this day and age the word beta has become such a gimmick that Gentoo is including so-called beta software as part of its core system. Back in my day beta meant beta and you had to walk 17 miles uphill both ways to get to the nearest phone jack. Mind you we didn't call them modems in those days, we called em clinkerdinkers....
Way to go, Internet.