[dwheeler]

Work done by US government employees as part of their official duties is in general not under copyright within the US.

But that is a much narrower statement.

Most software developed using government funds is not exclusively developed by government employees as part of their official duties. Most Government funding of software development goes to contractors, where that rule does not apply.

The no copyright only applies to the US, not necessarily outside. Outside the US it definitely can have a copyright.

There are also some weird exceptions for government employees, specifically for the u.s. postal service and for certain materials created by NIST.