blandflakes uses Java
Pretty much everything - Java is reasonably fast, reasonably safe, and reasonably expressive. I wouldn't call it the best at any of those things. The real advantage to me is that the virtual machine is ubiquitous and many people can understand it. Since I have the most experience in this language, it's my tool of choice for most projects.
I've also been learning JavaFx so that I can build user interfaces without the web. I've started several single-page-application projects that worked, but felt like workarounds or hacks and would be better-served as self-contained applications.
denkbar.io uses Java
Do I really need to explain? Well to me, the most appealing factor in Java besides the unbelievable community and vast array of available libraries, is just the amount of effort that has been put in the modern JVM. Decades of optimization and improvements have lead to a terrific piece of technology. I admire the people contributed to that.
Scrayos UG (haftungsbeschränkt) uses Java
Shouldn't surprise anyone, as minecraft is also java-based. Java is used for much more than just the plugins though. JCVortex (our API) is also served with vert.x (Java) and many of our team-internal tools also originated from java or are still java-applications.
Web Dreams uses Java
The most popular language in the world, definitely every programmer would use the Java language at some point. Frankly, I only use java when it’s a must. I find the language to be a little bit tedious when working with it.
brenoinojosa uses Java
bytelore.com makes extensive use of Java in its applications. We use Java due to its performance, community and the number of other projects built in the language. We have many projects and libraries built in Java.
papaver uses C
been programming in c for over a decade, since learning it in college. still use it for various low level projects. used it recently to develop an embedded application for a custom board.
micro systems uses C
The core of the arcapos applications is written in C, so are most of the Lua modules (bindings to various hardware or protocols).
Sqreen uses C
The Sqreen PHP agent is both a PHP extension, built in C, and a daemon built in Python.