Markdown:
[^1]
HTML generated by Markdown Extra (eg. as in Parsedown):
<sup id="fnref1:1">
<a class="footnote-ref" href="#fn:1">1</a>
</sup>
HTML generated by Multimarkdown (eg. as in Marked2):
<a href="#fn1" id="fnref1" title="see footnote" class="footnote" data-orig-id="fnref:1">1</a>
Markdown Extra looks more semantic but is harder to format.
Nice touch: tooltips in Multimarkdown – didn't test the „see footnote“ in other languages though.
Inline-footnotes are only possible via Multimarkdown.
Appropriate CommonMark thread.