Apart from access to a couple of additional protocols such as NFS, SMB and SFTP
via kde-base/kdebase-kioslaves, Krusader can use some external applications:

Tools

eject   - sys-apps/eject
locate  - sys-apps/slocate
kdiff3  - kde-misc/kdiff3
kompare - kde-base/kompare
xxdiff  - dev-util/xxdiff
krename - kde-misc/krename
kmail   - kde-base/kmail
kget    - kde-base/kget
kdesu   - kde-base/kdesu

Packers
arj     - app-arch/arj
unarj   - app-arch/unarj
rar     - app-arch/rar
unrar   - app-arch/unrar
zip     - app-arch/zip
unzip   - app-arch/unzip
unace   - app-arch/unace
lha     - app-arch/lha
rpm     - app-arch/rpm
dpkg    - app-arch/dpkg
7zip    - app-arch/p7zip

Checksum Tools

cfv     - app-arch/cfv
md5deep - app-crypt/md5deep