I want to run some different one-shot games for my group, to introduce them to a few different rule systems. We have primarily played d&d 3.5, Pathfinder, Shadowrun, and most recently d&d next/5e for our main campaigns. With our Shadowrun game ending in the next month or two, I want to run a handful of games with different systems, to try them out. Something new and fresh if you will. Do you know of any systems that work well for 1-shot games? I have done several dungeon world one-shots. I am thinking of doing an apocalypse world game, a Savage world one as well. Any others that are quick and easy, but could be turned into a 6+ month campaign if we really like it?

Fate Accelerated tends to work well for such games. And if the nice thing is if you want to turn things into a larger game, you can transition to regular Fate, or to a more robust system entirely.

A mortals New world of Darkness game? You can do a self-contained horror story.

Call of Cthulhu.

If done right, they are all basically 1-shot games
mwahahahaha

I was thinking FATE as well. I have played it a bit myself, but none of my players have.

Never even thought about CoC, though, yeah, I could see that only lasting 1 session or so! good call.

I have never touched on NWoD. Been meaning to check it out, so maybe I will do that. Any other suggestions out there?

Numenera.  You can explain the rules in under fifteen minutes, and have characters done in another fifteen, at absolute max.  The setting is also flexible enough to use elements from multiple genres (sci-fi, fantasy, horror, post-apocalyptic, even a touch of western).

I picked up The Strange a few days ago. I have not had a chance to delve into it too much. From what I understand it is essential Numenera, just with a more sci-fi twist rather than the fantasy/sci-fi/future world of the base game. I was not sure if it would work well as a quick game though.

1PG from Deep 7 Games. It was designed for 1 shots, but it makes a good, simple game for longer PbP campaigns too. It's my current fave rule set. It costs $4.

Mutants and Masterminds 2nd edition. If your group has done Shadowrun, they should have no problem with chargen in M&M. After that, since you've played D&D 3.5, they already know 80-90% of the 'during play' mechanics.

You could always check out Lady Blackbird. It's free and looks like a fun adventure with pretty simple mechanics.

Savage World's tagline is "Fast, Furious, and Fun", and it pretty much is, which means it can lend itself well to short/1 shot games.  Character generation for beginning human characters if pretty straight forward, and there's a dozen and a half well done archetypes if players would rather use pre-gens.

There's a bit of crunch to the resolution mechanics, but not nearly as much as something like Shadowrun or even Pathfinder so it should give a good balance without being too much for players to learn for a one shot.

Brave New World.

Minimal fuss.  Max excitement.

Paranoia.

Everybody Dies!!!!!

Stars Without Numbers is a pretty cool sci-fi RPG. The system is simple to learn, it's easily customized, and has a ton of tables you can use to generate NPCs, environments, planets, aliens, factions, etc. Try it for the system, keep it for the tables. Also, it's free.

I second Lady Blackbird. It's designed for one shot games. Also by John Harper, Danger Patrol Beta (or pocket edition). If you like 50's pop-sci (Flash Gordon) then you'd get a kick out of it. It's also very easy to reckon for other settings. John Harper has some other free to play games that are worth checking out.

Been gone, so I am to lazy to get caught up on my reading, but Talislanta seemed a good system for 1 shot games.

Call of Catthulhu but it's a game better played around a table with some friends rather than online.
It is really rule-lite so you can setup and play a 1-shot evening without major issue. :)