In Unix, applications can easily be combined to create higher-level applications. For instance, uncompress a database, select all lines beginning "Total:", and sum the second field of those lines to give a grand total:
zcat db.Z | grep "^Total:" | awk '{print $2}' | accumulate
(assuming a suitable definition of accumulate).

Unix has an impoverished data-model (lines of text), but even so this method of interoperability is very powerful. Similar techniques are next to impossible in current windowing systems.