She explained: "I was trying to figure out a way to show people how you can be complicit in a destructive system. That's all a game is, it's a system of rules. I never actually call it a 'game' – it's not enjoyable, you don't play it more than once.
"But when humans do something unspeakable to other humans, there is a system there too. Players have to feel like they made the decisions that sent those people to the camp.
"In this game, if you realise what's going on, you can break the system and save the people. It's more challenging, but plenty of people didn't go along with the rules in Nazi Germany."
Only one copy of the game exists, made up of three miniature but historically-accurate railway lines and carriages - which contain yellow people. The doors of the carriages are just wide enough to fit the figures inside, making players force their people into the trains.
Ms Brathwaite, who has worked on video games including Dungeons and Dragons, says seeing the game played is still difficult for her.
"It makes me sick every time a little person goes in that carriage, it literally turns my stomach."
Players control a train and move it along the tracks, picking up cards which describe obstacles preventing it reaching its destination - and players interpret the scenarios on the cards.
Ms Brathwaite said: "For example, when the train derails, what happens to the people? Do you blindly follow the rules? Or do you let them escape?"
A card at the end of the track reveals that the people have arrived at one of the death camps.
She added: "To me, it's blindingly obvious it's a game about the Holocaust, and most Jewish people know instantly. But many don't make the connection with the imagery and that's astounding to me, seeing as the Holocaust happened not long ago."
Train has won the Vanguard Award at Indiecade, a video games festival for "pushing the boundaries of game design".
It features in the latest edition of GamesTM magazine. One Jewish reader, Joel Waxman, from Borehamwood, said: "I'm going to cancel my subscription. You don't play a game about the Holocaust. It's tasteless."
Only once has a person not been deeply affected when they realised the game's objective, Ms Brathwaite said.
"It was utterly shocking, she picked up the card and it was Dachau. She unloaded her little people and put her train at the beginning of the track. I asked her, and she knew it was a concentration camp, and she said, 'It's just like a video game I know'. Her two co-players were just astounded. She came back later and said she felt embarrassed.
"The most powerful response was from a friend's rabbi, Rabbi Arnold Belzer, in Savannah, Georgia. He talked to me for about two hours, he wanted to know everything.
"At the end, much to my surprise he gave it a blessing as a work of Torah. I'll never do something that means that much again. I'm not planning on making money from the game. I don't want to put 15 million trains in boxes and sell them."
"However, there have been many requests for me to bring it to the UK, and I'll probably do that next year."
