What does 'software development kit' do?

I researched it and put it in my Engine but can’t find it anywhere, what does it do? It’s not in the wiki either.

IIRC, The SDK is what allows you to licence the engine out to other studios, thus getting a steady income from the it.

The newest Engine with an SDK included generates approx 3% of the complete Development costs of the Engine per month for some time.
When the Engine is growing old (2 years or so, don’t know exactly) the income generated slows down to a halt some month later.

Only the latest Engine generates this license income. And you have no choice of the receiving company.

They facilitate the creation of applications by having a compiler, debugger and perhaps a software framework . They are normally specific to a hardware platform and operating system combination. … For Universal Windows Platform the . NET Framework SDK might be used.