Mithril. Much simpler than anything else and batteries included. It's a great way to get beginners into front-end frameworks and gain knowledge that transfers easily.

Indeed. I use it to introduce beginners to modern front-end frameworks here: https://medium.com/front-end-hacking/how-it-feels-to-learn-j...

Mithril is nice. W.r.t. going for batteries included, it's still a bit minimal for my taste. Personally I would lean towards something more dogmatic, in the spirit of Rails. For example, things that I would miss from Ember: ember-data, models (with relations), controllers, opinions, integrated tooling, etc ... But Mithril looks cool I've been meaning to play with it too. You're right that skills gained from learning Mithril will be more widely applicable to general front-end dev than Ember.

How about rails?

Rails is great, but where it really shines is server side apps, content sites, blogs, CMSs, etc .. If you know you're building purely a SPA, Rails isn't really the right tool for that.

I'd argue that more than half pure SPAs do not need to be SPAs, and can be written effectively in Rails with someone who knows it well, in less time, with less bugs, and more test coverage.