Everybody know that in RTS games a player responsibility is to make war and such war is what “generates” fun for the player. But I was wondering if there are also other sources of fun in such games. I, for one, like to do research in RTS-es as it gives me sort of satisfaction to do a whole tech tree available in a mission.

What do you find in RTS games that gives you fun (besides war)? I'm looking for ideas :-)

Farming simulators like Stardew Valley come to mind. Time management games like Diner Dash. The various Tycoon games that are out there. I suppose it depends on what elements you consider as being central to an RTS. A vast amount of game run in "real time" (as opposed to turn based) and are simulations of some sort.

Another angle is providing sand-box and letting player decide what to do: Dwarf Fortress. DF is not an RTS (it's not ‘real-time’, and borderline ‘strategy’). I would rephrase DF's idea to the RTS genre as that:

“Create an environment with enough different mechanics that they are interesting to explore and combine; and create some adversity in the environment so player has guinnea pigs to test these interesting combinations”

Dwarf Fortress has some adversity indeed, but fortresses often fall by the player's hand.

Games with pretty deep management mechanics like those old Business Management Sims are always fun to me.

I think an RTS with more diplomatic possibilities, and robust supply chains in the vein of Anno could be fun if executed correctly.

Or something where the map rewards exploration and is for example procedurally generated.

A RTS can be scriptable enough to be modded into entirely different games that fit an overhead 2D map with realtime action. For example, I remember a Starcraft map that was Tetris (fitting groups of grid-aligned monsters into a rectangular loading bay).
Even within the boundaries of "combat" a great variety of experiences is possible, from tower defense to exploration, from winning frantically with high production rates to winning patiently with sniping, from sending off vast armies to micromanaging a handful of powerful units.

I guess it's not exactly RTS, but the Pikmin games come to mind as something similar where you are commanding a large number of various units (pikmin) to accomplish tasks like finding ship parts/treasure, and along the way you unlock new kinds of pikmin with different abilities. There is a time-management aspect to the game, where you need to accomplish certain tasks before the sun sets or else you lose pikmin. There is also combat with various creatures, but it's not really the main focus.