Office (spreadsheet, presentation, word processing) software
Libreoffice a free and open source office suite compatible with other major office suites, including Microsoft Office. Available for a variety of computing platforms, including Microsoft Windows, Mac OS X , and Linux-based systems. LibreOffice features a word processor (Writer), a spreadsheet app (Calc), a presentation program (Impress), a database management tool (Base), a vector graphics editor (Draw), and an app for working with mathematical formulas (Math). LibreOffice also includes a PDF creation and import tool for working with Adobe Portable Document Format (PDF) files.
R, which can be used with a graphic interface like R Commander and many more R is a free software programming language and a software environment for statistical computing and graphics. The R language is widely used among statisticians and data miners for developing statistical software and data analysis. Recommended book: Getting Started with R and any free manual. Also you can try online tutorials as this.
Zotero. is free and open-source reference management software to manage bibliographic data and related research materials (such as PDF files). Notable features include web browser integration, online syncing, generation of in-text citations, footnotes and bibliographies, as well as integration with the word processors Microsoft Word, LibreOffice, I also usa to store my notes and almost any kind of document from my computer. Really handy.
Document preparation system
Latex, with many editors, as LaTeXila, Lyx and my favorite: Gummy. Simply, LaTeX produced documents just look better. Latex is a document markup language and document preparation system for the TeX typesetting program. The typesetting system offers programmable desktop publishing features and extensive facilities for automating most aspects of typesetting and desktop publishing, including numbering and cross-referencing, tables and figures, page layout and bibliographies. The reason that LaTeX looks more refined and polished is that it is uses iterative typesetting algorithms which determine the optimal layout based on many typographical rules. Word processors are not written to typeset (i.e. determine the optimum position of characters/words) documents on the fly. Longetivity is another benefit of LaTeX. Documents written 20 years ago in LaTeX are just as usable and customizable as those produced today. Compare this with a document produced using a word processor from 20 years ago, it is likely the software no longer exists and if it does it has undergone so many changes that it may not display the document correctly.