OpenTTD is an open source remake of the 1995 game "Transport Tycoon Deluxe". In the game, the player must buy trains, buses, planes, and boats to transport people and goods in an attempt to make a profit. The game can be downloaded for free at openttd.org.
The game features singleplayer, as well as multiplayer, over LAN or online. There is also a scenario editor where players can create their own maps for playing. If there is not enough content, you can download mods inside the game.
On the Christmas Livestreams in 2011, it was the first game which was played, and it was played by Duncan, Sips (both of whom had newly formed channels), and Lewis. Lewis and Sips returned to the game on New Year's Eve, and were accompanied by Simon and Rythian (however, Simon and Rythian did not actually play.)
The game developers soon posted on their news to welcome Yogscast fans to the game.
Sips, Lewis, and Duncan played it in the 2012 Christmas Livestreams, and this time were accompanied by Ridgedog and Mexxy.
In September 2013 Lewis, Sjin, Duncan, Sips, and Ridgedog started another series. Posted on Sips' channel, it has been struggling for views. This series has been infamous for players sabotaging others, which comes in the forms of land locking docks, destroying NPC roads and buildings and trying to ruin companies holds on towns.
During the 2015 Christmas Livestreams, Lewis, Sjin and Duncan played for almost 6 hours, and raising over $37,000 during that time period. They stopped playing after they had raised $100,000 total.
During the 2016 Christmas Livestreams, Lewis, Sjin and Duncan once again played the game as per the yearly tradition. At the start of the game, the use of aircraft's was banned, though Duncan and Sjin later broke this rule in attempt to beat Lewis. At the end of the game, Sjin had made the most money.
On the first night of the 2017 Christmas Livestreams, as per tradition, Lewis, Sjin and Duncan played OpenTTD once again joined by Zylus for the first time. In the one evening, $1,068,123.86 was raised, a new best for the livestreams!