For me, only one was literally only one, I used the number 1 for entire game, points and power-ups. When u take a power-up, fow example your speed goes from 1 to 11 immediately. But same thing happens to your score too. So you need decide carefully while taking a power-up. They are a little much rewarding :D Here is the game, you can play and rate it!

/jam/gmtk-2019/rate/462865

My "One" is a flag, a blue flag.  You play as a little blue guy from a very blue land. It has been taken over by evil red guys, who have committed the horrible crime of wearing a different coloured shirt from you. What's worse is they have planted their repugnant red flags all across your beautiful blue land! This cannot stand. You will not rest until every red flag has been captured, and all the land secured under one flag, the one true flag, the blue flag!

/jam/gmtk-2019/rate/462780

My "Only One" was "Only One Resource": Hearts. They're your life, ammo, and timer. I also wanted to add dashing with the hearts being stamina, but I barely made the game as is in this timeframe.

Click HERE to play the game: HeartGame

I game that you can ONLY play ONCE (it is actually a meta-puzzle-game)

/jam/gmtk-2019/rate/461276

Only one developer, only one day (sigh), only one dimension (at a time)

https://doctormikereddy.itch.io/thomas-was-a-line and /jam/gmtk-2019/rate/462856

Can only move in 1 direction, entire game including menu's and level built into only 1 Unreal level.

Our game is build around "Only one damage" or "Only one strength" concept.

We came up with a pretty cool damage effect. It's a lot of fun. And I still stuck at level 18.

https://santazaaa.itch.io/hyper-slash

Originally I was planning to make a mixology game where there was only one drink you could make that wouldn't cause your patron's head to fall off, but the files all got corrupted and I didn't have time to finish -_- - so I made a crafting game, Decrafted (/jam/gmtk-2019/rate/463986) where the objective is to craft your way down to one item rather than up to as many as possible

For my game If (/jam/gmtk-2019/rate/461616), an Gameboy RPG game, started with: one action button, one character and one place.

In the end finish with one action button, one character, one place, one enemy, one NPC and one battle.

We made a two-player game called Cyclopia featuring shooting  with only one eye. Literally with one single eye you could not perceive the depth. But you can estimate the distance of the bullet from other hints to bounce off back your opponent like Genji.

I did one huge map xD /jam/gmtk-2019/rate/460859

I did  a text adventure titled "Only One Day", where you live your final day before the end of the world! Jolly, right?

https://brownseededbread.itch.io/onlyoneday

For my solo roguelike project, the only one thing was only one item in inventory :D

Our two person team dug up a rough concept we'd been kicking around but never done anything with. "You had ONE job" is a multiplayer, arena/horde based game where you can only do a singular thing. Shooting, or looting (we wanted to add "defending/healing" but ran out of time). The idea is that you can't accomplish anything on your own. If I keep working on this I want to improve individual player scoring and maybe to end game callouts (Like Overwatch in its voting) and implement the missing class, and generally improve the feeling of you doing a singular thing and playing a role in a larger team.

/jam/gmtk-2019/rate/461546#post-854292

Here it is if anyone wants to take a look, be warned that controllers and multiple people are kinda required to get any kind of experience out of it. Probably not the best for a game jam game but we're endlessly inspired by couch co-ops like Overcooked and Ultimate Chicken horse.

"LASER" As the minimalistic title of my game suggests.

https://guillemsrr.itch.io/lsr

I wanted to pick an idea that would be seemingly impossible with "only one." I ended up doing a text adventure with only one word, and I think it turned out pretty well! /jam/gmtk-2019/rate/461221

In Whiteboard Arena my "only one(s)" were: one vs one with one keyboard, only one action (jump), only one screen, last one standing.

/jam/gmtk-2019/rate/461347

For our game, a maze with only one exit: /jam/gmtk-2019/rate/463810

Sp00ky game where you have only one second to see at a time (lightning strikes)!

/jam/gmtk-2019/rate/463099

For me it was make a platformer with 'Only One' thing to climb. I wanted it to be a creature, but ended having to settle for on massive and complicated wall instead, i learned a great deal about design in the process!

https://newkryptonite.itch.io/the-lonly