Duplicate Files Finder : http://doubles.sourceforge.net/
For Windows and Linux. Lets user find dup files (by their content, not only their names). The search can include and exclude files (ex.: exclude all *.tmp) and restrict which file sizes are searched.
Can remove dup files by deleting them or by creating links.
Instead of using hashes, it uses the following algorithm:
The algorithm is as follows: First, all files are sorted by their size, because files can be only equal, if they have the same size (logically). Then the files are compared with each other, and thus the equal files are determined. If two files are not equal from a given point on, reading is interrupted; no more has to be read for determining that these files are not equal. Because of this the results are determined much faster than in programs which use hashing algorithms, for which all files have to be read completely. Additional caching of the contents of the files additionally improves performance.