When it comes to RDD, Qt (C++), Symfony (PHP), Django (Python) are the best choices.
Need to patch a Bitcoin fork ? Or may be a ERC20 contract for Ethereum ? We write those as well.
When it comes to develop software, TDD and BDD are not optional. They're mandatory. No testing ? Then no code.
SQL or bigdata ? PostgreSQL, MariaDB, Cassandra, CouchDB, Mongodb, HBase/Hadoop are our friends when it comes to store your data.
Linux (Debian, Centos), Unixes (FreeBSD, OpenBSD)... Wherever your code needs to work, it will work.
Firewalls, systems hardening, cryptography... We do those everyday!
A software is not just line of codes, it's also tests, revision control, bugtracking, build automation, continuous integration...