I am working with an author that needs two different footnote streams. This can quite easily be done by using bigfoot.
EDIT Also note that the margins used are narrow, like 10mm or so. Therefore the 2nd stream should be "under" the text.
I did things like that :
\documentclass[a5paper,11pt]{scrbook}
\usepackage{geometry}
\usepackage{perpage}
\usepackage[ruled]{bigfoot}
\MakePerPage{footnote}
\renewcommand{\thefootnote}{\alph{footnote}}
\DeclareNewFootnote{A}[arabic]
\begin{document}
Lorem\footnote{a footnote stream} ipsum dolor sit amet, consectetur adipiscing elit.
Vestibulum ut lorem\footnote{a footnote stream} ligula. Pellentesque eget nibh quam.
Etiam molestie iaculis dictum. Ut fringilla odio quis quam aliquet egestas. Nam
dignissim ante eu nibh bibendum, a laoreet ipsum\footnoteA{another footnote stream}
aliquam. Donec euismod erat ac malesuada sodales. Fusce viverra feugiat ligula vel
rhoncus. Aliquam erat volutpat. Nullam consequat sollicitudin quam, id dapibus tellus.
Nulla tempus mattis justo, eget aliquam elit vehicula sed.
Curabitur ante felis, rutrum sed sem nec, fringilla rhoncus metus. Mauris blandit, dui
non tempus porttitor, sapien urna fermentum ligula, nec molestie dolor lacus vel
ipsum\footnoteA{another footnote stream}. Maecenas odio enim, vulputate sit amet nulla
nec, laoreet imperdiet sapien. Cum sociis natoque penatibus et magnis dis parturient
montes, nascetur ridiculus mus. Integer sed tincidunt dolor. Nunc laoreet interdum
condimentum. Maecenas neque urna, porttitor ac neque id, gravida cursus odio.
In egestas lobortis nisi eu malesuada. Donec leo nibh, vulputate vel arcu vel,
adipiscing pharetra ipsum\footnoteA{another footnote stream}. Maecenas vitae augue
luctus, ultrices nisi sed, hendrerit ipsum\footnoteA{another footnote stream}.
Suspendisse potenti. Mauris id blandit arcu, et sodales massa. Sed laoreet dapibus
lectus id bibendum. Nunc eget orci id lectus auctor sagittis. Vivamus tincidunt semper
mattis. Curabitur quis lorem\footnote{a footnote stream} tortor.
Sed volutpat urna ligula, eget posuere neque condimentum eu. Integer feugiat erat ac
lorem interdum, ut pharetra quam blandit. Nulla blandit sit amet tellus at cursus. Nam
eget eleifend felis. Aliquam pulvinar mi sit amet magna gravida congue. Mauris
pellentesque dui et turpis laoreet dictum. Donec commodo ultricies risus, eget
fringilla sapien hendrerit eu.
\end{document}

But the author is asking me if there is any possibility of having one stream beside the other and not below the other.
And of course if only the second stream is present in a given page, to have it on the right alone.

Any way to achieve this ? I tried to use scrextend package that helps me in settings the left and right margins of the footnote, but that does not seem to solve my problem.

twocolumnoption is given to the standard document classes anddblfnote.styfor inspiration --- though neither do anything close to what you want. – jon Jul 22 '14 at 16:04memoirregularly. It is a great class, but what you are trying to achieve is likely an order of magnitude more difficult than simply achieving two-column notes. It is, sadly, beyond my ability to help.... – jon Jul 23 '14 at 15:33