Guacamole is a Java program. It's basically a proxy between RDP/VLC and HTML5. Guacd (the java bits) connect to an RDP or VNC server on your behalf, and then you interact with the remote machine through guacd. Here's a simple text diagram

  [Windows RDP server] <--RDP protocol--> [linux Guacamole server] <--HTTP or Websockets--> [HTML5 client in your browser]

Wait.. so you're saying you need a linux server to access your windows server?

That's the configuration I use. You can run guacamole directly on the target server if you want. I'm reluctant to expose my Windows machines directly to the wild internet, and I don't want to learn how to configure an HTTPS reverse-proxy in Microsoft's ecosystem. Having a dedicated guacamole box is nice because I expose port 80/443 on my Linux Guacamole machine, and then use it to connect to any number of Windows and Linux computers behind my firewall/NAT.

Ok I see, thanks for the explanation.

That seems to be the case. Under "How do I get it?" it says:

> You will need a Linux or UNIX computer to host Guacamole.

I'm guessing that since it's java, you can run guacd on either windows or linux.

Only the web application is Java, guacd is written in C:

http://guac-dev.org/doc/gug/guacamole-architecture.html

From the github readme:

  > guacamole-client is used to build the subprojects that  make up Guacamole, and
  > to provide a common central repository. Each project contained here is
  > completely independent of guacamole-client and can be built separately, though
  > the others may have to be built first. If all projects are built using
  > guacamole-client, Maven will take care of the proper build order.

My reading of this is that the client repo also contains the server, which is written in java

Server side is java