\documentclass[11pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{authblk}
\usepackage{enumitem}
%\usepackage[bottom=0.5in]{geometry}

\title{Title of seminar or poster}

\author[1]{\underline{name of speaker}}
\author[2]{name of second author}
\author[2]{name of third author}
\affil[1]{affiliation of speaker}
\affil[2]{affiliation of second author}
\affil[3]{affiliation of third author}

\begin{document}
\date{}
\maketitle
\thispagestyle{empty}

Text of the abstract.
It should fit one page.

\begin{enumerate}[label={[\arabic*]},labelindent=\parindent, leftmargin=*]
  \item First reference
  \item Second reference
\end{enumerate}

\end{document}

