Affinity Photo has a range of tools - mirror is one of their filters and this can be used to create symmetrical designs using a photo as well as paths etc and also brushes. Any brushes. In this video, one set of brushes are used and this is then mirrored in a variety of ways. Video shows the creation of a spray paint brush stroke 2) changing of colors in the Affinity Photo 3) Using the filter menu 4) Using the mirror filter and mirrors 5) Re-applying the mirror filter 6) Blending modes and fade 7) Deform filter combination with mirror and more.
More info about the app via the Serif site but also via http://www.graphicxtras.com