R's data.table package extends data.frame:

Read-only mirror of R source code from https://svn.r-project.org/R/, updated hourly. See the build instructions on the wiki page.

Lightweight extension of the base R graphics system

reproducible benchmark of database-like ops

A lightweight version of R Markdown (without using Pandoc or knitr)

reproducible benchmark of database-like ops

A minimal benchmark of various tools (statistical software, databases etc.) for working with tabular data of moderately large sizes (interactive data analysis).

A place to work on documenting recent algorithmic improvements to data.table.