The best alternatives to Assemble are Nifty, Height, and ActiveCollab. If these 3 options don't work for you, we've listed a few more alternatives below.
What do you think of Assemble?
AssemblyAI— Multilingual Speech-to-Text API with superhuman accuracy
Height is the autonomous project collaboration tool. With an embedded AI engine, Height handles the legwork of building products on autopilot. Offload soul-sucking chores like bug triage, backlog grooming, and documentation updates for good.