Believe it or not I never actually used restic, even to this day, I think only became aware of it around 1.5 years ago when somebody using Kopia asked me about comparison.
I’ve been experimenting with building what is now Kopia for >5 years now (btw it used to be called “FREDI” which stood for “fast, remote, encrypted, deduplicated, incremental” backup). Initially it was meant to be more of a personal research project than a practical tool. I’ve been working for Google Cloud since 2012 and I became fascinated with the potential for very cheap and virtually unlimited and highly-available storage. I wanted to build not just a cloud backup utility, but first and foremost a properly-layered, fully client-side encrypted, multi-user, content addressable storage without a dedicated server (so only using GCS or S3). You can still see remnants of it in https://github.com/kopia/repo
Over the early years I was experimenting with organizing the repository (or “vault” as it used to be called) and tried, wrote&rewrote and renamed things a lot. I think went through maybe 3 or 4 major ideas for packing, index organization, object naming, splitting, compression, encryption.
Around 0.3 timeframe when it became clear I’m onto something, I started focusing more on polishing the user experience, adding HTML-based UI and things became usable enough to be able to finally get rid of my CrashPlan dependency on all my computers around the house.
At this point (with 0.6.0 release out very shortly), Kopia has almost all the core features I originally envisioned in a personal/LAN backup solution.
Since Kopia started recently getting more serious adoption and contributions from Kasten and others, we started focusing more on robustness, performance, resource utilization, safety, etc. We just got major Garbage Collection safety and performance improvements in.
In addition to what we have today, for v1.0.0 I want to be able to have endurance tests for bigger repositories (10TB+), complete the UI and finish support for remote repositories with sharing/deduplicating data amongst folks where there’s not complete trust (imagine LAN or a dorm room situation).
What’s beyond is largely up to community - folks are already trying to push Kopia in some interesting directions and I’m sure more of that will come.