its fascinating to me how historical vedic religion and the brahmins were influenced by buddhism (elucidation and emphasis on dhyana in india were popularized by the buddha as well as his contemporary patanjali) as well as jainism, besides the obvious non-vedic puranic influence on what became hinduism (which is itself very diverse). indian religions, even sikhism, use closely related terms and concepts, though buddhists in particular like to emphasize where they are different.

i find sikhism is less known than other indian religions. its a non-evangelist monotheist (but with brahmanical-esque pantheism too) religion centered around a combination of spiritual devotion/bhakti as well as right action/karma, which mirrors the unity of temporal and spiritual life represented by the twin swords. it was perfectly situated in its context of hindu-muslim strife and persecution (which led to the archetype of the warrior-saint as well) but also in the overlapping conceptions of god that sufism and nirguni bhakti have. and the message of striving for personal excellence, service, and devotion above claiming a one truth makes it a morally excellent creed for all times, even though obviously it does consider itself a revealed religion. it does not have particularly developed system/sadhana for internal work like in strands of buddhism or hinduism as far as i know, but its emphasis is on bhakti yoga and recitation/singing. they use gurus in sort of a subversive way too, with a line of ten gurus who offer specific insight and then the line breaks/continues forever with the final guru which is their holy book.