In that case, let's compare apples with apples- the final release of XP was in 2008. So we're looking for software released on or before 2001, actively develope

In that case, let's compare apples with apples- the final release of XP was in 2008. So we're looking for software released on or before 2001, actively developed until 2008, then on life support since then. On the other hand, many oss projects have rolling releases, so trying to compare like this is futile, expect for the fact they have been maintained for a very long time. LaTeX 2e has been around since 1994 and is still the current, maintained version.