Opera (Optimal Paired-End Read Assembler) is a sequence assembly program (http://en.wikipedia.org/wiki/Sequence_assembly 
). It uses information from paired-end or long reads to optimally order and orient contigs assembled from shotgun-sequencing reads.
An updated version called OPERA-LG has been re-engineered with features for the assembly of large and complex genomes.
Song Gao, Denis Bertrand, Burton K. H. Chia and Niranjan Nagarajan. OPERA-LG: efficient and exact scaffolding of large, repeat-rich eukaryotic genomes with performance guarantees. Genome Biology, May 2016, doi: 10.1186/s13059-016-0951-y.
Song Gao, Wing-Kin Sung, Niranjan Nagarajan. Opera: reconstructing optimal genomic scaffolds with high-throughput paired-end sequences. Journal of Computational Biology, Sept. 2011, doi:10.1089/cmb.2011.0170.
https://genomebiology.biomedcentral.com/articles/10.1186/s13059-016-0951-y
