Deen literally means the way of life.
And the only acceptable way of life is Islam, Submission to God's Will (i.e. the Quran) - 3:19.
Dharma of Indians, and Asha of Zoroastrians (and perhaps Chinese Qi) may be very close to Shaa'a (شاء) of the Quran, that is, Will of God = order/laws of nature = Divine Laws.
But today, the only preserved, pure and true Deen is Islam, and its only source is the Quran.