List of wiki engines taken from [Wiki Popularity].  Also see [Line breaks].

!!!Summary as of 10 Jan 2007

!!Double backslash
* Confluence
* DokuWiki
* JSPWiki
* PmWiki
* SnipSnap

!!BR surrounded by double square brackets
* MoinMoin
* MoniWiki
* TracWiki

!!!Most Popular Open Source Wiki Engines

!![MediaWiki]
{{{<BR>}}}
!![Twiki]
{{{%BR%}}}
{{{<BR>}}}
!![TikiWiki]
{{{%%%}}}
!![PukiWiki]
{{{ &br; }}}
!![MoinMoin]
{{{[[BR]]}}} (a macro)
!![PmWiki]
{{{\\}}}
{{{[[<<]]}}}
!![DokuWiki]
{{{ \\ }}}
!![PhpWiki]
{{{%%%}}} [PhpWiki Text Formatting Rules|http://phpwiki.sourceforge.net/phpwiki-1.2/index.php?TextFormattingRules]
!![MoniWiki]
{{{ [[BR]] }}}
!![TiddlyWiki]
does not exist?
!![JSPWiki]
{{{ \\ }}}
!![SnipSnap]
{{{ \\ }}}
!![WackoWiki]
{{{ --- }}}
!![Xwiki]
does not exist?
!![UseMod]
{{{<BR>}}}
!![Oddmuse] 
Varies. {{{<BR>}}}, {{{\\}}}, and single newlines (blog-style) have been used.
!![Midgard Wiki]
does not exist?
!![FlexWiki]
does not exist?
!![Zwiki]
does not exist?
!![TracWiki]
{{{ [[BR]] }}}

!!!Most Popular Commercial Wiki Engines

!![Confluence]
{{{ \\ }}}
!![PBwiki]
does not exist?
!![Socialtext]
does not exist?
!![Wikispaces]
does not exist?
!![StikiPad]
does not exist?

!!!Other Wiki Engines
!![MicKI]
!![ProWiki]
!![SdiDesk]
!![WikkaWiki]

!!!Other Markup

!!Textile
!!LaTeX
{{{\\}}}
{{{\\*}}}
{{{\newline}}}
!!HTML
{{{<BR>}}}
!!XHTML
{{{<br/>}}}