being selected for release). Carmack has continued to advise developers to be careful when depending on middleware, noting how it can limit the possibilities of later releasing source code. Tim Sweeney has implied this issue has hindered potential releases of older Unreal Engine source code. This led not only to source ports that allowed the playing of the non-free games based on these engines (plus fan added enhancements) on free engines and systems, but also to new free games such as Freedoom, Blasphemer, Open Quartz, LibreQuake, Nexuiz/Xonotic, Tremulous/Unvanquished, Quetoo, OpenArena, and also Uebergame on the later open sourced Torque engine. Freeware games, such as Harmony, The Adventures of Square, Alien Arena, Warsow / Warfork, World of Padman, The Dark Mod, and Urban Terror, have also taken advantage of these free engines and sometimes have given code back to the community. Development and editing tools are also commonly released freely, such as GtkRadiant, Qoole, Doom Builder, LibreSprite, LDtk, Tile Studio, and Tiled. Released engines have also been used for fangames such as Sonic Robo Blast 2, Wolfenstein: Blade of Agony, and ZBlood/Transfusion, and even commercial games such as Wrath: Aeon of Ruin, Steel Storm, and DOOMBRINGER, on the DarkPlaces engine, as well as Hedon, Selaco, and Vomitoreum on the GZDoom engine and also titles by Blendo Games on the id Tech 2 and id Tech 4 engines. id partners and related, such as Raven Software, Bungie and 3D Realms, as well as several of the developers who participated in the Humble Indie Bundle, have also released code and it is now accepted practice for some mainstream game developers to release legacy source code. Formerly proprietary games such as Jump 'n Bump, Dink Smallwood, Clonk, Seven Kingdoms, AstroMenace, Warzone 2100, Glitch, Maelstrom, Planet Blupi, Avara, Eat the Whistle, Blades of Exile, Star Control 2, SimCity, Fish Fillets, HoverRace, Duelyst, as well Abuse and the unfinished Golgotha have even been entirely released freely, including multimedia assets and levels. Some games are mostly free software but contain some proprietary content such as the Cube sequel, Sauerbraten (and later forks such as Red Eclipse), or the former Quake III Arena mod Smokin' Guns, but some developers desire and/or work on replacing these with free content. Released source code has even been used for commercial re-releases of vintage games such as Wolfenstein 3D Classic for iOS, Abuse Classic for iPhone, and The Original Strife: Veteran Edition.