Author and year displayed in separate column: which bibliography style is this?

You can automate the choice of length with the following code

\newcounter{mymaxcitenames}
\AtBeginDocument{%
  \setcounter{mymaxcitenames}{\value{maxnames}}%
}

\newlength{\citelabelwidth}
\defbibenvironment{bibliography}
  {\list
     {\begingroup\defcounter{maxnames}{\value{mymaxcitenames}}\usebibmacro{cite}\endgroup}
     {\setlength{\labelwidth}{\citelabelwidth}%
      \setlength{\leftmargin}{\labelwidth}%
      \setlength{\labelsep}{\biblabelsep}%
      \addtolength{\leftmargin}{\labelsep}%
      \setlength{\itemsep}{\bibitemsep}%
      \setlength{\parsep}{\bibparsep}}%
      \renewcommand*{\makelabel}[1]{##1\hss}}
  {\endlist}
  {\item}

\makeatletter
\AtEveryCitekey{%
  \blx@setlabwidth{\citelabelwidth}{\usebibmacro{cite}}
}
\makeatother

This is similar to what biblatex does with numeric and alphabetic labels already.

MWE

\documentclass{book}
\usepackage{geometry}
\usepackage[utf8]{inputenc}
\usepackage{filecontents}
\usepackage[backend=biber,style=authoryear,maxcitenames=1]{biblatex}

\newcounter{mymaxcitenames}
\AtBeginDocument{%
  \setcounter{mymaxcitenames}{\value{maxnames}}%
}

\newlength{\citelabelwidth}
\defbibenvironment{bibliography}
  {\list
     {\begingroup\defcounter{maxnames}{\value{mymaxcitenames}}\usebibmacro{cite}\endgroup}
     {\setlength{\labelwidth}{\citelabelwidth}%
      \setlength{\leftmargin}{\labelwidth}%
      \setlength{\labelsep}{\biblabelsep}%
      \addtolength{\leftmargin}{\labelsep}%
      \setlength{\itemsep}{\bibitemsep}%
      \setlength{\parsep}{\bibparsep}}%
      \renewcommand*{\makelabel}[1]{##1\hss}}
  {\endlist}
  {\item}

\makeatletter
\AtEveryCitekey{%
  \blx@setlabwidth{\citelabelwidth}{\usebibmacro{cite}}
}
\makeatother

\renewcommand*{\nameyeardelim}{\addcomma\space}

\begin{filecontents}{biblio.bib}
@article{lamport1982byz,
  title={The Byzantine generals problem},
  author={Lamport, Leslie and Shostak, Robert and Pease, Marshall},
  journal={ACM Transactions on Programming Languages and Systems (TOPLAS)},
  volume={4},
  number={3},
  pages={382--401},
  year={1982},
  publisher={ACM}
}
@article{lamport1998part,
  title={The part-time parliament},
  author={Lamport, Leslie},
  journal={ACM Transactions on Computer Systems (TOCS)},
  volume={16},
  number={2},
  pages={133--169},
  year={1998},
  publisher={ACM}
}
\end{filecontents}
\addbibresource{biblio.bib}

\begin{document}
\cite{lamport1982byz} 

\cite{lamport1998part}

\printbibliography
\end{document}

MWE">

Here's a version with biblatex, because I find that natbib is really hard to customize.

For now, the length is manual (set to 100pt) since this is the first time I've been trying to change biblatex this much and I'm not sure how to set it automatically. Although I doubt you should have longer last names, if they happen, you can just slightly increase that length. In the meantime, here are the results.

Output

Code

\documentclass{book}
\usepackage{geometry}
\usepackage[utf8]{inputenc}
\usepackage{filecontents}
\usepackage[backend=biber,style=authoryear,maxcitenames=1]{biblatex}

\DeclareFieldFormat{labelalphawidth}{#1}

\defbibenvironment{bibliography}
  {\list
     {\printtext[labelalphawidth]{%
    \printnames[][-\value{liststop}]{labelname}\addcomma\space%
        \printfield{labelyear}}}
     {\setlength{\labelwidth}{100pt}%
      \setlength{\leftmargin}{\labelwidth}%
      \setlength{\labelsep}{\biblabelsep}%
      \addtolength{\leftmargin}{\labelsep}%
      \setlength{\itemsep}{\bibitemsep}%
      \setlength{\parsep}{1.5ex}}%
      \renewcommand*{\makelabel}[1]{##1\hss}}
  {\endlist}
  {\item}

\renewcommand*{\nameyeardelim}{\addcomma\space}

\begin{filecontents}{biblio.bib}
@article{lamport1982byz,
  title={The Byzantine generals problem},
  author={Lamport, Leslie and Shostak, Robert and Pease, Marshall},
  journal={ACM Transactions on Programming Languages and Systems (TOPLAS)},
  volume={4},
  number={3},
  pages={382--401},
  year={1982},
  publisher={ACM}
}
@article{lamport1998part,
  title={The part-time parliament},
  author={Lamport, Leslie},
  journal={ACM Transactions on Computer Systems (TOCS)},
  volume={16},
  number={2},
  pages={133--169},
  year={1998},
  publisher={ACM}
}
\end{filecontents}
\addbibresource{biblio.bib}

\begin{document}
\cite{lamport1982byz} 

\cite{lamport1998part}

\printbibliography
\end{document}