The analysis shows:

1. the choice of **..** and //..// for bold and italic is collision free
2. {{...}} for images collides with following wikis:
   1. MediaWiki for templates
   2. Confluence for mono
   3. JSP Wiki for mono
   4. Wikispaces for mono
   5. StikiPad for mono
3. {{{...}}} collides with MediaWiki template parameters
4. == for headings has two partial collisions:
   1. TikiWiki where ===...=== is used for underline
   2. DokuWiki where the heading order is reveresed, that is ===== is a level 1 heading
5. [[link|text]] has a partial collision with TiddlyWiki
6. *... (bulleted list) has a collision with PukiWiki where it is used for heading
7. #... (numbered list) has a collision with Midgard Wiki where it is used for heading
8. <<...>> has a collision with TiddlyWiki, where it is used for macros

Please add the collisions with markup of wiki engines you know!