Maybe the first program you may use. It reads a set of mapping given by the tool you have used to map your data on the reference genome and translate it to a set of genomic coordinates. You also have the possibility to extract only those that you are interested in (few matches in the genome, few errors in the mapping, etc.). You can also select those reads which map less than a given of times in the genome. Moreover, you can output the data in various different formats, which you can use to visualize them via UCSC genome browser or GBrowse. Unmatched reads can be written in an other file, in case you would like to try to map them with another tool (may sometimes work!).
You can filter your data according to:
The script needs an input file (your mapped reads) together with its format and the read sequences file together with its format (FASTA or FASTQ). If you want, you can also append the results of this script to another GFF3 file. This is useful when the GFF3 file is the result of the mapping using another tool.
By default, any gap in the alignment to the reference sequence is treated like an exon. You can decide to remove this feature by merging short introns (actually, gaps).