Newbie table formatting/numbering question

Question

I'm trying to format a table like the following:

0.0a summarry       b other summarry
                      (long)
 .1a junk           b more junk
1.0a etc            b so forth

Ie, with all the contents top- and left-aligned and everything lined up semi-nicely and the main columns the same size.

So far the best I've been able to come up with is:

\documentclass{minimal}
\usepackage{amsmath}
\usepackage{fontspec}
\usepackage{array}
\setmainfont{DejaVu Sans}
\title{---}
\date{}
\newcolumntype{T}{>{\vtop\bgroup\vspace*{-\ht\strutbox}\hbox\bgroup}
                   c<{\egroup\egroup}}
\begin{document}
  \begin{tabular}{ T T T l T l }
    \hline
    0&.0&a&
    summary
    &b&
    other summary (long)
    \\ \hline
    &.1&a&
    junk
    &b&
    more junk
    \\ \hline
    1&.0&a&
    etc
    &b&
    so forth
    \\ \hline
  \end{tabular}
\end{document}

Answer 1

\documentclass{article}
\usepackage{amsmath}
\usepackage{fontspec}
\usepackage{array,ragged2e}
\setmainfont{DejaVu Sans}
\begin{document}
\begin{tabular}{ r @{} l >{\RaggedRight}p{3cm} r >{\RaggedRight}p{3cm} } \hline
    0.0 &a&  summary &b& other summary (long)        \\ \hline
     .1 &a& junk     &b&  more junk \\ \hline
    1.0 &a& etc      &b&  so forth  \\ \hline
  \end{tabular}
\end{document}

Answer 2

\documentclass{article}
\usepackage{booktabs} % <--- for drawing rules
%--------------------------------------
\begin{document}
  \begin{tabular}{p{.05\textwidth}p{.4\textwidth}p{.03\textwidth}p{.4\textwidth}}
    \toprule
    0.0a & summary   &b & other summary (long) \\ \midrule
    0.1a & junk      &b & more junk            \\ \midrule
    1.0a & etc       &b & so forth             \\ \bottomrule
  \end{tabular}
  %--------------------------------------
\end{document}

Answer 3

It isn't clear what output you are trying to make with the \vtop construction (which isn't really LaTeX at all). It makes each entry a single line with odd vertical alignment. Your suggested output appeared to show 4 columns but the code has 6? If it alternates between a numeric column and a longer description, perhaps tabularx and lXlX is what you are looking for

\documentclass{article}
\usepackage{amsmath}
%\usepackage{fontspec}
\usepackage{array,tabularx,dcolumn}
%\setmainfont{DejaVu Sans}
\title{---}
\date{}


\begin{document}
 \centering
 \begin{tabularx}\linewidth{D{.}{.}{-1}llXlX}
    \hline
    0.0&a&  summary    &b&  other summary (long)
    \\ \hline
    .1&a& junk &b&  more junk
    \\ \hline
    1.0&a& etc    &b&    so forth
    \\ \hline
  \end{tabularx}
\end{document}