All (shimano) 8sp-10sp derailleurs are compatible (possibly excluding duraace, which has a different cable pull). Mountain and road. Almost all 11sp clusters (shimano, sram, campy) are cross compatible with derailleurs. The basic shimano hyperglide freehub will generally work with 8-11sp clusters, possibly requiring a spacer.
If you're willing to go friction (bar end), you can run a mid 90's 8sp Shimano 600 short cage rear derailleur on a 10sp 12-28 rear, with a 1x39 in the front.
If you're willing to go friction (bar end), you can run a mid 90's 8sp Shimano 600 short cage rear derailleur on a 10sp 12-28 rear, with a 1x39 in the front.