few Microsoft Windows users. Open source games have also been made available for Android and iOS mobile devices. Frozen Bubble, originally a clone of Puzzle Bobble, has become a classic known for its addictive gameplay and winner of many Linux Journal Reader's Choice Awards. These games and others have also helped expand the prevalent Tux genre which started with titles and like A Quest for Herring and are related to the activist content of games like XBill. As well as ground up clones, open source re-implementations of various proprietary games have also become increasingly common, which utilize the original game data. More original games like kiki the nano bot, Danger from the Deep, Tanks of Freedom, Tetzle, Teeworlds, osu!, Avoision, Alex the Allegator 4, Chromium B.S.U., Amphetamine, Slune, Zorn, Dynamite, Battle Tanks, M.A.R.S., Balls Blocks and Mazes, Free Tennis, Powermanga, the Geki series, the Enemy Lines series, Worminator 3, Abe's Amazing Adventure, Adventures on Plante Zephulor, Cow's Revenge, B.A.L.L.Z., The Powder Toy, Nikwi, Me and My Shadow, Which Way Is Up, Stringrolled, Endgame: Singularity, and C-Dogs, have also been able to carve out their own niches. Strategy and simulation games have also been a prevalent force in free software gaming, partly due to the lack of proprietary options for free software operating systems as compared to other genres like first-person shooters and role-playing games. Xconq and XBattle, and later Freeciv and Lincity, began the trend, and were followed by other clone titles like FreeCol, UnCiv, C-evo, LordsAWar!, Freelords, OpenCity, TripleA, Mindustry, OpenRA, OpenRCT2, OpenTTD, Simutrans, Tenes Empanadas Graciela, Thousand Parsec, Unknown Horizons and Widelands. The Stratagus project began as an attempt to recreate the proprietary Warcraft II engine, under the name FreeCraft. Blizzard Entertainment sent a cease and desist letter in 2003 over the use of the name "craft" in comparison to Warcraft and StarCraft. Though the earlier free software strategy game CRAFT: The Vicious Vikings shared the name "craft" without controversy. With the new, legally inoffensive name Stratagus and the old FreeCraft assets renamed Aleona's Tales, the team began work on a new strategy game called Bos Wars. Development on this game still continues, as well as the modern Warcraft II port Wargus. Other games branched out of the engine project as well such as the Battle for Mandicor and Astroseries projects, the StarCraft port attempt Stargus, and most recently Wyrmsun. After the Stratagus example, other real-time strategy games