Ruby, Ruby on Rails
Gems: devise, carrierwave, cancan, simple_form, formtastic
Template engines: erb, slim, haml, liquid
JS: jQuery, CoffeeScript
CSS: compass, sass/scss
Servers: unicorn, passenger, nginx
Testing: rspec, cucumber
DB: mysql, postrgesql, postgis, MongoDB, redis
Hosting: Heroku, amazon web services
Maps: openlayers, openstreetmap, Google maps, Bing maps
High load: sharding, balancing, replication, caching, scaling, profiling, benchmarking, monitoring