Also known as "the Wanderer," Renddar is a goddess specific to iddun mythology. Said to be represented by a constellation in the sky that moves the most as the night goes on, Renddar is a goddess that instills the desire to wander and see more of the world.
As an iddun goddess, Renddar is thought to be an iddun herself. She is said to have stars in her wings and scales, and she is accompanied by a host of spirits. These spirits are said to be blessed by her so that they can see things they could not experience in life.
The principle doctrines of Renddar largely revolve around expanding one's world and learning new things. They have several taboos against being "tied down," which would limit one's ability to wander and learn new things; consequently, although they build temples to house knowledge from all across the galaxy, there are very few buildings affiliated with this religion. Wandering followers of Renddar may set up tents temporarily when they move into a new area, but they're designed to be able to be taken down quickly and without leaving anything behind.
For similar reasons, followers of Renddar often do not have families. This is less due to a celibacy-related doctrine and more because in conservative iddun society (where the religion began), one would be expected to not abandon any children they bring into the world. Consequently, families are viewed as something that bogs down people and roots them in one place, making them complacent in where they are. Although most followers of Renddar would say that the "no family" rule only applies to clergy within the religion, some zealots may actively sneer at anyone who gets "too tied down".
While Renddar followers tend to be more lenient towards machinery than most iddun institutions, many of them are still wary of it. It may have the potential to do good, such as spread information and aid in travel, but it has the potential for great evil as well. Consequently, only higher-ups in a given temple are trusted to handle machinery, and most lower acolytes stay away from it.
Renddar's temples tend to be pretty open to other gods and ideals because in their minds, being closed off would go contrary to Renddar's teachings and desires for people to wander and learn new things. Because they're "stuck" at the temple, as it were, it's good for them to expand their worldview and acknowledge other gods. If a traveler were to stop at their temple, they wouldn't think anything of the traveler offering a word of prayer to their own god instead of Renddar there.
Followers of Renddar would roll their eyes at monotheists (even those who say Renddar is the only god in existence, because that's really close-minded and, in their eyes, certainly not true). Most of them don't see anything wrong with monolatrists, as they're sometimes monolatrists themselves (monolatry being the worship of one god while still acknowledging others). Many priests who worship Renddar also worship others just as a matter of encountering religions that are congruent with their worldview, and it's not uncommon to encounter polytheistic priests and priestesses of Renddar.
When worshipers of Renddar spread their goddess' word, they are often baffled by other religions finding their proselytizing offensive. In their minds, Renddar's teachings are completely compatible with those of other faiths; after all, there's no reason to live in a closed-off world, and actively believing in other gods and participating in other religions would be good in Renddar's eyes.
In many ways, the faiths that believe in Renddar are closer to a philosophy than a religion, though they still have some sacred texts and rites, particularly for funerals to send spirits to wander with Renddar. They still caution against many other people's worldviews that are materialistic, as such things tend to cause someone to be rooted in one place. After all, investing a large amount in an expensive house would make you want to stay there instead of continuing to travel. However, a part of this warning is certainly due to the typically xenophobic nature of iddun society, and followers of Renddar who are not idduns often disregard this aspect of the religion.