gzipcompression utility, or alternatively
bzip2that you find on ftp://sunsite.unc.edu:/pub/Linux/utils/compress; this tool compresses better than
gzip, but it's also a wee bit slower and consumes a lot of memory;
upxexecutable compressor, whose home page is at http://cdata.tvnet.hu/~ml/upx.html and http://wildsau.idv.uni-linz.ac.at/mfx/upx.html;
zlibcpackage, available on ftp://sunsite.unc.edu:/pub/Linux/libs/compression. It's called
X.Xis the latest version.
There are other executable compressors. One is
gzexe (forget it), while
tcx was probably the best before
upx became available; yet another is
tzx, in theory better than
tcx. The thing is, it screwed everything up when I tried it on a spare PC, though I'm not sure if I did something wrong. You had better stick with
upx: it's reliable, efficient, and very handy.
There are kernel patches that provide transparent file system compression a la Stacker, but as of this writing none of them has yet a reputation for stability and reliability. For safety's sake, steer clear.