The megasquirt is the DIY solution to engine management, they are a good product if you know what you are doing, you can buy kits or assembled boards. I would buy the kit and solder it up on my work bench but that is me, I have a bit of electrical know how despite what I thought about what I used to think I knew
It does have a lot of features but be prepared to spend some late nights on the simulation mode just tinkering with the variables seeing what works and what doesn't. I have not spent more than 5 minutes with one but it is the same as any stand alone setup you have some fuel maps and ignition maps on the screen in front of you and you tune them according to different variables to make a 3d/4d/5d....up to however many dimensions you like within reason. I looked at the maps for my uncles drag car once, I think it hurt my brain enough that permanent damage was done
It is just one of those things where the more you know the better off you will be in the long run. Getting an engine running on a stand alone setup is easy, getting it running correctly to make horsepower without damaging the engine is the difficult part. That is why dyno time is expensive, your paying for collective knowledge from a lot of expensive engines (and a lot of expensive f*** ups)