This reminds me of 37Signal's [1] & ZachHolmans [2] talk about Your Product is your Byproduct. Real eye opener on how to think about what you're building and/or identify cross promotion etc.

[1] - https://signalvnoise.com/posts/1620-sell-your-by-products

[2] - https://zachholman.com/talk/product-is-the-byproduct/