A recent JDK, Groovy 2.3 or so, Grails 2.4 or so, Eclipse with the STS plugins for Groovy and Grails, running on Fedora Linux or CentOS. PostgreSQL 9.x database. KDE desktop environment, bash shell. For front-end stuff, pretty much just JQuery and Bootstrap. But I'm not primarily a front-end guy, so I don't get as deep into a lot of the different javascript tools and stuff as some people. I do like Hopscotch for building product tours though.

Angular is on my "to learn" list, and I'm always working to learn more about CSS.

For data-crunching on the backend: Hadoop 2, Hive, Pig, Impala. Kafka. Storm for real-time stream processing stuff.

Other "go to" libraries / tools:

Lucene for search

Tika for document parsing

HornetQ for JMS / message queuing

Activiti for workflow / BPM

Camel for message routing

On the "to evaluate / learn" list: Spark, Samza