[gshenaut]

I too am interested in this. I tried using OP in this way, but having to think in terms of specific units of time is just too annoying. Even if dates are undetermined, you still have to specify the duration of each task. If OP could use “undetermined” as the effort/duration of some or all tasks, but keep the sequences and dependencies, it would be great. Alternatively, there could be a kind of timebase based on non-time units, like “chunks” or “steps” or whatever. Being able to mix determined and undetermined duration tasks would also be great. Obviously this would be a pretty big change to OmniPlan. (I agree that OP is probably a better tool than OG for this, by the way.)