Thirteen years of R/qtl: Just barely sustainable

R/qtl is an R package for mapping quantitative trait loci (genetic loci that contribute to variation in quantitative traits) in experimental crosses. Its development began in 2000. There have been 32 software releases since 2002. The latest release contains 35k lines of R code and 24k lines of C code, plus 15k lines of code for the manual pages. A key to its success is that it remains a central tool for the chief developer's own research work, and so its maintenance is of selfish importance.