Plugins are mainly user-contributed add-ons that enhance and extend TWiki features and capabilities. A limited number of plugins are included in the core TWiki distribution - and most those can be removed - while the rest are optional, available from TWiki:Plugins/WebHome.
Here is a list of the plugins currently installed on this TWiki site:
SpreadSheetPlugin(any TWiki, $Rev: 18078 (02 Sep 2009) $): Add spreadsheet calculation like "$SUM( $ABOVE() )" to TWiki tables and other topic text
AccessStatsPlugin(9 Apr 2007, $Rev: 15560 (12 Dec 2008) $): Provides statistics by parsing access log file, such as Apache access log
CalendarPlugin(Dakar, $Rev: 14775 (11 Dec 2008) $): Show a monthly calendar with highlighted events
CommentPlugin(03 Aug 2008, $Rev: 17791 (02 Sep 2009) $): Allows users to quickly post comments to a page without an edit/preview/save cycle
DatePickerPlugin(2015-01-10, $Rev: 28649 (2015-01-11) $): Pop-up calendar with date picker, for use in TWiki forms, HTML forms and TWiki plugins
EditTablePlugin(4.9.1, $Rev: 18014 (02 Sep 2009) $): Edit TWiki tables using edit fields, date pickers and drop down boxes
EmbedPDFPlugin(2011-05-10, $Rev: 21206 (2011-05-11) $): Embed PDF documents in TWiki pages
HeadlinesPlugin(2.4, $Rev: 18156 (30 Sep 2009) $): Show headline news in TWiki pages based on RSS and ATOM news feeds from external sites
InterwikiPlugin(28 Feb 2009, $Rev: 14913 (17 Sep 2007) $): Link ExternalSite:Page text to external sites based on aliases defined in a rules topic
MultiEditPlugin: (disabled)
NewsPlugin(Dakar, $Rev: 15565 (12 Dec 2008) $): %NEWS% generates a short headlines topic from a list of news