PartMetFS is a user space filesystem based on FUSE, to mount the Temp directory of emule and clones. On the mounted directory we see the real name of the file being downloaded and, depending on the file type, we can open the file as if it were complete.

In case of AVI files, the index is rebuilt in a way not to include the missing parts of the file. Like this, we can watch the part of the AVI already downloaded.

The idea is to create these kind of adapters for other types of files and be able to make previews of them.

SourceForge PartMetFS site