Nick Kallen, an early Twitter engineer and author of Arel, writes about Rails, ORMs, caching and software modularity.
HN links his 'Why I wrote Arel' post when discussing ORMs, and his cache-money write-up and defense of Java-style abstraction.
It's been a long debate, and yes, it's almost like sequel. Actually, ARel positions itself into the same niche as sequel, i.e. low-level toolkit to build frameworks on.
In my opinion, sequel is an absolute kick-ass sort of thing, it's just that ultra-cool if you have time and will to hack.
Further reading:
http://sequel.heroku.com/2010/02/06/arel-sequel-differences-part-1/
http://sequel.heroku.com/2010/02/10/arel-sequel-differences-part-2/
http://sequel.heroku.com/2010/02/23/the-benefits-without-the-costs/
http://magicscalingsprinkles.wordpress.com/2010/01/28/why-i-wrote-arel/ -- note comments bout sequel
As a counterpoint, I like this quote from Twitter's Nick Kallen:
This smacks of the oft-ridiculed Java AbstractFactoryFactoryInterface. But let me put it bluntly: AbstractFactoryFactoryInterface's are how you write real, modular software–not little fart applications.
http://magicscalingsprinkles.wordpress.com/2010/02/08/why-i-love-everything-you-hate-about-java/
[N.B. I'm not saying there isn't a lot of truth in the factorial article, it's just you have to know which challenges just need a one-liner function and which require an AbstractFactoryFactoryInterface]
dhh, tenderlove, wycats: purveyors of an anti pattern!
In all seriousness, I'd love to see a criticism of ORM that takes Arel into account (http://magicscalingsprinkles.wordpress.com/2010/01/28/why-i-wrote-arel/). I have yet to see one.
I believe it just uses it under the hood, but I'm not familiar enough with relational algebra (or ARel) to know for sure. Here's a blog post from the author:
http://magicscalingsprinkles.wordpress.com/2010/01/28/why-i-wrote-arel/
cache-money is great idea for a plugin. the author has a really good write up of it:
http://magicscalingsprinkles.wordpress.com/2008/12/11/introducing-cache-money/
Also a blog post from the author about Arel here:
http://magicscalingsprinkles.wordpress.com/2010/01/28/why-i-wrote-arel/