Nebu: A Lightweight Spreadsheet Editor for Varvara

Nebu is a lightweight graphical spreadsheet editor for the Varvara system, designed to handle csv/tsv files. Math operations are performed by specifying a rectangular range of cells followed by an operator. A range is defined using a colon between two cell identifiers. A cell performs at most one operation, and the range must precede the cell and cannot recursively include itself. It supports basic arithmetic (+, -, *, /), counting non-empty cells (#), and string concatenation ("). If no operator is specified, it defaults to summation. Nebu launches instantly and weighs less than an empty Excel file.