I use Cinelerra mainly. Both Cinelerra and Kdenlive are videos editors. They have lots of overlap in a lot of functionality. I am trying to fully switch to Kdenlive, but it is taking time. I use blender to create 3d titles and other fun effects. I use slowmovideo for ultra slowmovideo video. The final product looks just as good as twixtor to me. However, slowmovideo does take a little more work to learn. You won't find too many tutorials out there for it.