The topic under discussion has mostly been about lighter mobile artillery pieces; the US landing guns, other 3-inch guns and pack howitzer - all more or less infantry support weapons used before and during WW2.
I'm no expert on artillery but I have a favourite: The Nordenfelt* Maxim 37 mm auto cannon better known as the "one-pounder" or "Pom Pom" of the late nineteenth century.
The Pom Pom was used with great effect by the forces of the Boer republics during the South African War and later also adopted by the British, but despite showing immense promise as an infantry support weapon, it met a dead end just before the First World War.
Instead, the 1-pounder Pom Pom evolved into an anti-aircraft gun, ultimately resulting in the eight barrel 2-pounder AA gun as used aboard RN ships during WW2. Its original role was forgotten, and I'm not aware of it or any similar weapons seeing use after the First World War. A good on-line article here:
Sure this weapon had its limitations but it could have been quite useful (I think) for the conditions experienced in the Far East and Pacific during WW2. What you think guys?
* sometimes spelled Nordenfeld or Nordenfeldt