We expect the highest similarities with Jainism. There we find many of the Buddhist superlatives: arihant, nirvana, buddha. Of course they are embedded in their own Jain frameworks with different meanings. But most probably these terms were not uniquely Buddhist but were part of a common samana spiritual vocabulary.
I have not come across the same four stages anywhere else. But I also wouldn’t expect it. According to some research (and here there will be disagreement) sotapanna and arahantship are the oldest stages, and sotapanna might go back to a Buddhist conversion formula. Meaning, the sotapatti could have originally been the convert who entered the stream of Buddha-Dharma, and thus would be rather exclusively Buddhist.
Joy Manné (1995). Case Histories from the Pāli Canon, II: Sotāpanna, Sakadāgāmin, Anāgāmin, Arahat–The Four Stages Case History or Spiritual Materialism and the Need for Tangible Results. Journal of the Pali Text Society, 21, 35-128
See also Sakadāgāmi, opapātika, anāgāmi. Are they late concepts i.e. not EBT?
The Brahmins had two end-goals: In the late Brahmanas and Upanisads it was realizing atman, and apart from that rebirth in the eternal brahmaloka.