Both come from Mentor Graphics.
Questasim is 32 or 64bits like modelsim. The name have changed when new language like e, sv, ams... have been supported by Mentor. By behind this, that is the same engine.
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and after that you have Questasim or Advance MS package, both of them have Questasim behind, the second are "ready" for mixed simulation with spice model, connected to Eldo simulator.