Efforts have been put so far in different directions. This may have been general bug fixing, like correcting issues or adding features to Cura. Once the troubling line of code has been found, the solution for the problem can be found pretty close. Therefore, the most direct way is being taken and fixing the bugs myself. Another (and maybe the biggest) field of interest is the development of plugins.
CAD integration plugins:
Do you think rapid-prototyping cannot be faster?
Take a look at the offered CAD integration plugins and benefit from saving time. This way you can get more room for creativity, more intuitive designs and faster iterations when constructing technical parts!
Visit the CAD integration page to get known of all benefits and features, which make you more time-efficient and more successful, when loading your CAD files into Cura.
Cura PPA for Ubuntu Linux
Important note since Ultimaker Cura 4.x:
Ubuntu 18.10 “Bionic” is needed as a minimum, but I recommend using Ubuntu 19.04 “Disco” as I’m using this version and can deliver fixes faster.
If you are interested to inform yourself about installing Cura via PPA and benefit from regular updates provided via APT. Take a look at the separate page with further info and installation guidelines.
Other plugins
I’m also experimenting with developing other kinds of plugins. Some topics have been saving GCode to Toshiba AirFlash cards, printing over Ethernet (raw socket), etc. However, these projects have been stopped due to leak of time.
CuraDevelopmentKit (dead)
A lot of time has been put into the CDK. The idea was to have an SDK-like environment that represents the software environment of Cura but keeps the ability to develop your own applications easily. A lot of knowledge has been earned around CMake and the other build systems, but the project got so time-consuming that I had to drop it.