Trekker Online is brand new and works for us.
As a starter I was able to create and share a trek with my friends for free. There is a license fee if I want to create more treks or publish to the public but one private scavenger hunt is enough for now.
It let me locate and design the sites using my phone's GPS locator and it was easy to create puzzles, instructions, hidden caches and photograph opportunities. There's not many trails on Trekker yet but it should become very popular.
Here's the website address: trekker.online