Bikepacking.com has posted a summary, state of the market sort of article on smartphone apps that can enable the use of one's smartphone as a GPS.
Also a free subscription to GaiaPro on offer ...
If you have other suggestions please add them. Hopefully we can turn the thread into an on-going resource on the topic.And we have great news… After getting in touch with Gaia regarding this post, they’ve offered one year of their GaiaPro subscription free to any readers of Bikepacking.com. GaiaPro can be used as a standalone service on gaiagps.com, or as an enhancement to the mobile app if you choose to purchase it. To redeem this offer, simply email support@gaiagps.com and mention bikepacking.com.