I found it for free on Steam; I didn't really understand the game at all, but I know one of you will get the most out of it and enjoy it :D

This one holds special place in my heart. Created by Pandemic Studio (THAT Pandemic studio) in 2002, it offers a unique take on Army Men Series.
You command plastic soldiers, fighting other plastic soldiers in everyday environments, e.g. backyard, kitchen e.t.c. Unit roster is pretty generic: Rifle soldiers, Bazooka soldiers, Tanks, Half Tracks.
Every RTS lover needs to play this at least once.

This one is kinda odd but fun. What If scenario for WW2. 3 Factions (USSR, Germany and US). Build your base, construct a massive army and attack your enemy. Classic C&C Formula. What stands out the most - the Weird World War aspect. You got huge assault zeppelins, walking mechs, frost bombs, dual rotor helicopters, that kind of stuff. Red Alert style.

As I assume many here, I grew up during late 90s / early 2000s RTS boom.

First strategy game I ever played was the OG AoE demo found in a Win98 disk.

At the time I was playing: AoE, EE, Cossacks, Stronghold, C&C, Imperium, RoN and other "mainstream" ones.

Recently, I came across Warzone2100 and got really into it (it's also FOSS now so that's great)

Any other, less mainstream ones, I might have missed at time, that you guys consider must-plays?

Are Earth2140/2150 and Seven Kingdoms any good?