Some interesting postings on Consimworld about Retro ASL: Gary's variant uses an IGO-HUGO sequence of play, most apparent (and surprising initially) is the absence of opportunity type fire as such. Rather, an INSPIRED game mechanic of 'hesitation' that causes units moving within Line of Fire of certain weapons to test for hesitation. If they pass, they may continue to move, if they fail. they stop - simple, tense and excellent for solitaire play.