Sword of the Stars has a more or less fixed tech tree, but your scientists can completely fail to find techs at random, sometimes locking you out of important technologies. Turns out that making a core gameplay mechanic RNG based is kind of annoying.

I liked the one in the old Stars! game where you invest in broad categories (chemistry, biology, etc...) and tech would unlock at a combination of tech levels. A better laser might be electronics 4, metallurgy 2 for example.