Scrapyard Engineers is a lot of fun

Splitsie's Scrapyard Engineers scenario is pretty great, I've been enjoying it, and if you haven't tried it, it's worth a crack.

The concept is that you basically don't get refiners or assemblers, and only a limited number of blocks you can make. Everything else, you have to find from wreckage strewn about the landscape. The goal is to get to space.

In addition to the base modpack, I strongly recommend Improvised Experimentation. The author also recommends it, but tunes down the carry weight so that you have to use cranes more. I didn't, but a crane is still extremely useful.