It is a python package for visualizing the RNA-seq data.
sashimi_plot is a utility for automatically producing publication-quality plots for RNA-Seq analyses of isoform expression. It is part of the MISOframework. In particular, sashimi_plot can: (1) plot raw RNA-Seq densities along exons and junctions for multiple samples, while simultaneously visualizing the gene model/isoforms to which reads map, and (2) plot MISO output alongside the raw data or separately.
The MISO framework is described in Katz et. al., Analysis and design of RNA sequencing experiments for identifying isoform regulation. *Nature Methods* (2010).
see here
http://genes.mit.edu/burgelab/miso/docs/sashimi.html