Kona is the open-source implementation of the K programming language. K is in the APL family of languages. If you are an expert programmer who doesn't know an APL but wants to learn one, then this is the place to start. The K language is ASCII-based so you don't need a special keyboard.
For many people, K is the preferred APL dialect. It tends to be popular with investment bankers, the performance obsessed, analysts with endless data, blasé experts, and other smart people with not a lot of time. K is a vertical language, meaning, fewer machines and fewer keystrokes do the same job, at the expense of a higher clock rate. It is a demanding language.
K was originally designed by Arthur Whitney and Kx Systems. Praise for K should be taken to refer to Kx's K. Kx sells a popular database called KDB+. People can and do create networked trading platforms in hours. If your business needs production K support, you can evaluate KDB+ prior to purchasing from Kx, or possibly speak with Kx consulting partner First Derivatives.
Kx's KDB+ uses the Q language, and is built on top of K4. Kx used to sell a database called KDB, which used the KSQL language, and was built on top of K3, an earlier K. To the confusion of all, these terms are used interchangeably. Kx's K3 is basically no longer available. Kona is a reimplementation of that K. Kona targets K3 but includes features from K4 and elsewhere. Kona is unaffiliated with Kx.
Windows
You can find an executable version of Kona here.
Build from source
Navigate to the file you want to install Kona, then type:
git clone https://github.com/kevinlawler/kona.git
cd kona
make #gmake on BSD
Then once in the file run:
./k #./k_test for debug mode
You can find further information about Kona at the wiki.