I knew
7-zip was an excellent open-source compression program (and library), but the last time I checked (which was years ago),
WinRAR was slightly ahead in text compression ratio. However, I downloaded the latest one and tried today, and it seems to have overtaken WinRAR.
I compressed the JDK 6 documentation from Sun, and the sizes were:
Uncompressed - ~265MB (12499 files, 851 folders)
Zip (original download format) - ~56MB
RAR (v3.71) - ~25MB
7-zip (v4.65) - ~20MB
Mind you, this were all text files. I didn't try with binary files but as I recall, last time I try with binary files and 7-zip
did compress binary files better than WinRAR. Also the WinRAR version I have is not the latest, while the 7-zip version is the latest (cheat!). You might also notice that both RAR and 7-zip beats the pants off standard zip.
Anyway, that's enough convincing for me: fully open source, with a permissive license, good GUI, and now possibly the best compression ratios of all: I'm switching over to 7-zip. So its Goodbye to shareware WinRAR and Hello to open-source 7-zip!