Some manual transmissions do use ATF, but not ours. The manual transmissions in our cars use SAE 75W90 gear oil, API spec GL4 or GL5. Dexron III is not suitable. Nor is any automatic transmission fluid, with the possible exception of
Redline's D4 or D6 ATF which are both rated as GL4 gear lubes.
The Pennzoil stuff you are thinking of is probably GM Synchromesh Transmission Fluid. Pennzoil supposedly produces this and sells it under their own label as well. It is not ATF and is not suitable for power steering either. Strictly for manual transmissions. The GM stuff is pretty popular with the Civic crowd, probably because it is less expensive than the Honda brand fluid. I've been running it in my 5 speed for 5 or 6 weeks now and it works well, with lower shift effort at low temperature and a quieter, more positive shift feel than the Syntec 75W90 I was running.