It depends. In my experience, most demos stay up, and the few that are taken down sometimes explicitly say so on the store page or demo announcement.

Neverlooted Dungeon: Comedy dungeon crawler inspired by games like Ultima Underworld and Arx Fatalis. The demo consists of a tutorial and a small open-ended area to explore, with a focus on avoiding traps and interacting with physics objects to navigate and find loot. The demo doesn’t really show off Arx-levels of complexity, but it’s fun to explore and genuinely funny at times.

Stop Dead: Fast paced first person shooter where you attack enemies by using telekinetic powers to hurl objects and bodies to deal damage. The weapons work kinda like Mirror’s Edge, in that instead of getting your own loadout you pick dropped guns up off the floor and get rid of them once they’re out of ammo. Also, if you stop moving for more than a moment, you die. Demo is quite varied, and ends with a challenging mid-game level to show off the mechanics a bit more.

Mr. Run and Jump: Challenging 2D platformer with a lot of different moves that can be chained together in slick ways. There’s not much of a narrative and the neon visuals kinda look dated in a not-even-retro way, but the movement really carries the whole game.

Echo Point Nova: New shooter by the developers of Severed Steel. Has a lot of the same mechanics (slow motion, destructible terrain, etc), but makes the levels a lot more open and adds a grappling hook and hoverboard for a different style of mobility. There’s a bit of jank, but it’s very satisfying to play.

El Paso, Elsewhere: Indie Max Payne. I’m not exaggerating, it plays like Max Payne 2 and looks and feels like Max Payne 1. Swap out the main character and it could pass as a phenomenally faithful fangame.

Phoenix Springs: Stylised neo-noir narrative-driven point and click adventure. I usually don’t have the patience for these sorts of games, but I found the writing and visuals very compelling.

Fortune’s Run: Sprite based RPG FPS with level design that feels a bit like the classic Deus Ex, but with the fast paced combat of a boomer shooter. Has a Star Warsy rough and gritty sci-fi setting, if you’re into that.

The Next Fests are my favourite Steam event by far, already looking forward to the next one!