The MMORPG engine Xtremeworlds, with either a previous version or a closely-related predecessor called Playerworlds, written by Brady O'Keefe around early 2006 and abandoned in late 2013, stored most of its game-specific (that is, excluding graphics, audio, etc., which appear to have been stored in standard, wider-context formats) data in files with the extension ".pwx". Most of these appear to be similar enough that they are presumably of the same format, or variations of the same format; in particular, all the files of a certain type (e.g. shops, inventory items, quests) will have the same size, with the end of most (or even the entire file, if unused) being filled with zeroes. Xtremeworld scripts written in Visual Basic also take on the extension ".pwx".
See also Xtremeworlds map.
- Version 1.0.4
- A search for zip files at mmorpgmaker.org in the Wayback Machine will get more versions.
- : An interview with Brady O'Keefe (2009)
-  The Playerworlds website
- : The first Xtremeworlds website
- : The second Xtremeworlds website
- : A reference for the scripting API
- ↑ https://web.archive.org/web/20090129191745/http://mmorpgmaker.vault.ign.com/index.php?option=com_content&view=article&id=46:xtremeworlds-2d-mmo-creator&catid=34:interviews&Itemid=59
- ↑ Date of https://web.archive.org/web/20060613034554/http://playerworlds.org/, the earliest entry in the Wayback Machine
- ↑ https://web.archive.org/web/20160401141017/http://mmorpgmaker.org/?title=Main_Page indicates that a release from late 2013 sat as the latest one for 3 years, before the website was taken down altogether