Charles Ouweland designed and built his own simple DIY active load, that is available on Github:
At first I was messing about with some big resistors but then I decided it would be nice to have an “active load” that you can set to a particular current. You can buy these things for quite some money but I decided to design and build myself a simple one using components and tools I have lying around. I decided to go analog, no digital stuff this time.
See the full post on Charles Ouweland’s blog.