btrfs-debug-tree (8) - dump btrfs filesystem metadata into stdout
btrfs-send (8)       - send data of subvolume(s) to stdout/file.
bzcat (1)            - decompresses files to stdout
Capture::Tiny (3pm)  - Capture STDOUT and STDERR from Perl, XS or external pr...
ip6tables-save (8)   - dump iptables rules to stdout
iptables-save (8)    - dump iptables rules to stdout
screendump (1)       - dump the contents of a virtual console to stdout
stdout (3)           - standard I/O streams
zipnote (1)          - write the comments in zipfile to stdout, edit comments...