What are the lightest and most portable nail guns?

This Metabo HPT cordless straight finish nailer uses an air spring drive system and brushless motor technology, with a 13% lighter, smaller tool body for easier maneuverability. It drives 16-Ga straight finish nails from 1 in to 2-1/2 in at up to 3 nails per second, with a selective actuation switch for sequential or bump fire modes. It includes an 18V 2.0Ah battery and is designed for trim and finish work.

The Metabo HPT NT1865DSA/NT1865DAA are cordless 18V brushless finish nailers that use an air spring drive system for pneumatic-like performance with fast, consistent driving. The 16-gauge model (NT1865DSA) is 5.7 lbs without a battery and drives up to 3 nails per second, using a 100-finish magazine and a selective actuation trigger. They suit professional trim and finish work where portability and light weight matter.

Milwaukee's M12 FUEL 18-gauge compact brad nailer (model 2541-20) is a cordless, brushless nailer built for tight spaces, using a nitrogen air spring for consistent depth. It can drive 5/8 to 1-1/2 in brad nails and has tool-free jam clearing and depth adjustment. It supports both sequential single firing and bump firing, with a lightest-weight claim of 4.6 lbs when paired with an M12 2.0Ah battery.