- Meteor. This is both a front and a back end system. It has a very cool reactive programming paradigm that runs all the way back to the data, and a killer package manager built in. It is built on Node and Mongo, and I have high hopes for it.
- AngularJS. HN linked to a great rundown on SO on how Angular differs from jQuery. Angular also uses reactive paradigm that allows the programmer to extend HTML for their application. Powerful stuff.
- Ractive. This is very, very new but it looks quite good. The concepts are Angular-like but the code looks better, and the excellent tutorials show that the author really pays attention to detail.
It's a visualization library, but D3 (probably better called D3.js or D3js so as not to be confused with Diablo 3, etc) deserves a mention. I'm particularly fond of this very well done D3js tutorial site. D3 is a bit of an odd duck because it really doesn't really do much on it's own; however it's creator, Mike Bostock, seems to be very productive with it and he creates some amazing visualizations with it. I'm still excited about it, since I started with Prefuse and then Flare and now D3 is the latest incarnation in that line of visualization tools.
On the size/performance/page size area, I recently ran across zepto and pure css. Zepto is a jQuery replacement that basically sacrifices browser compatibility for size. It weighs 5-10k vs jQuery's 50k. Pure is a pretty CSS framework that weighs in at a svelt 4.3KB - and I think it has 90% of the functionality I want from projects like Bootstrap. Having state-of-the-art JS and CSS support in a page under 10k makes me happy.
And now for something completely different: RethinkDB. This project strikes me as the Meteor of NoSQL DBs. Rethink is what Mongo should have been. The docs are extremely well-written, the team seems solid and directed, and I wouldn't be surprised if Rethink displaces Mongo as king of the NoSQL.