Front End
React-JS, AngularJS, AJAX, Bootstrap, SASS, LESS, JavaScript, HTML 5, CSS3
Back End
Java, Python, PHP, R, Ruby on Rails, Scala, GoLang, REST full API, WebSockets, WebRTC, SignalR, Web Services, WebAPI, OAuth, Spring, NHibernate, Hibernate, YII, Laravel, iText, pd4ml, Play Framework, NodeJS
IoT, Low level dev. libraries
Visual C++, C++, C, Boost,, WxWidgets, QT, Assembly language
Mobile
Objective-C (iOS, Mac OS), Flatter, Swift, Android SDK, ReactNative
Servers
Apache, Nginx, Apache Tomcat, GlassFish, Jetty, Netty, WildFly, IIS
Build
MAVEN, ANT, Gradle, SBT, Composer