Astro Command

Most browser "RTS" games are clicker-grade. This one plays like StarCraft-lite in a tab: mine minerals, build barracks and a factory, tech into marines, rangers, and tanks, and push across a fogged map to level the enemy command center.

The controls are the real ones. Ctrl+1-9 bind control groups, A is attack-move, box-select and shift-queue orders work like you expect. Turrets hold your line. And the AI opponent isn't a timer, it ramps its own economy, builds tech buildings, and times attack waves against you, scaling with the Easy/Normal/Hard setting you pick.

No install, no account, no build step, one HTML page. Pick a difficulty and a map size, and play a full round on a break.