What are some alternatives?
When comparing Rockstor and ngrok, you can also consider the following products
OpenMediaVault - OpenMediaVault is the next generation network attached storage (NAS) solution based on Debian Linux.
Portmap.io - Expose your local PC to Internet from behind firewall and without real IP address
FreeNAS - FreeNAS is a storage operating system strong and robust enough to meet the needs of enterprise level businesses.
Pagekite - Bring your localhost servers on-line.
Amahi Home Server - Amahi is a media, home and app server software known for its easy-to-use user interface. Amahi has the best media, backup and web apps for small networks.
Serveo - Use SSH to expose local servers over the internet and inspect and replay HTTP traffic.