Gregory's ServerI might be mistaken, but I feel like it adds another layer of lock-in as well. Now, not only can the file format be proprietary, but the use is linked entirely to the web site as well.
Google Drive is good about making downloads in several *usable* formats.
Canva (for example) much less so. PressBooks (for "open content" books) even less so, imo.
Local software and local data.
If only #k12 educators would understand this.