Keybase is amazing, and I'll be installing it on my mobile device. It really makes crypto a lot more approachable for average users. Their chat is great, and I'd been looking forward to the mobile app.
On desktop my only complaint so far is that they keep trying to jam everything into a single app. I think they could break things up into three separate apps: core, chat, and KBFS. Personally, I have no use for KBFS and I wish I could disable it. It's also slightly buggy on macOS, and it causes a warning messages to show when restarting.
I just tried to use chat on FreeBSD (helpfully mentioned in another comment) but it fails with "error unboxing chat message: KBFS client wasn't found" so they might be more tightly linked than you hope.
On desktop my only complaint so far is that they keep trying to jam everything into a single app. I think they could break things up into three separate apps: core, chat, and KBFS. Personally, I have no use for KBFS and I wish I could disable it. It's also slightly buggy on macOS, and it causes a warning messages to show when restarting.