It could be Senecio mandraliscae...it may not be getting enough sunlight, even if you think so. Indoors light away from the window is considerably lower than on windowsill and even less than outdoors. Few days of cloudy weather should not cause etiolation. These senecios naturally grow long stalks, but the leaves are quite sparse & far apart - that's why I think it needs more light.

Your plants are nicely arranged, just make sure that there is no water sitting under all that peat; and the white square container should have drainage hole.

That Senecio is extremely etiolated and in desperate need of more light. That species really wants full sun and as such isn't much of a houseplant. However, don't just stick it in full sun. You have to increase the light levels gradually.

Got it. Thanks guys! So surprising considering it does get direct sunlight a few hours a day...

Full sun outdoors is so different from what gets indoors. It isn't easy to tell, but you could see easily by plants response. Do as Nil suggested - first, in some light shade for few days, and move into more sun every few days.

Full sun is outdoor, direct sun (not thru the leaves or similar things) and min 6hrs/day. Longer is better :) Depending on where you are, noon could be really scorching for some plants.

Or might be Senecio cylindricus (aka S. vitalis). All it needs is a lot more light than it is getting.

A "few hours a day" is not "plenty of sun" by the standards of many cacti/succulents. People frequently make the mistaken assumption that because the light seems bright to their eyes that it must be bright by plant standards. As others have noted, your plants growth is saying otherwise. Just remember to harden it off gradually to much stronger --preferably outdoors-- lighting ....not unlike how a fair-skinned person needs to gradually expose themselves to strong sunlight after long cold winter if they wish to avoid serious sunburn.

It does need a brighter location but even then any added brightness and for longer periods of time of brightness does very little for the current etiolated top part(s). It might be a good idea to cut the stringy part back and propagate from the cuts with a better brightness/ lighting plan from the start.