I've recently revived a project I started well over a year ago - a  
Squeak client to the Generic Object Oriented Database System  
(http://www.garret.ru/~knizhnik/goods.html).  This is a nice, public  
domain database server, that provides fast, robust, transactional,  
distributed storage for objects from any language (although the object  
model maps especially well to Smalltalk).

If you've used Magma, the client has a similar feel - it's completely  
transparent (use your existing objects), only loads objects as needed  
(and can flush them from the cache if they're not being used), and  
automatically detects changes during a commit.  It's also considerably  
lighter weight than Magma (I believe the GOODS client has about 1/7 as  
much code as the Magma client), and provides a few extra features (like  
per-object read/write locks).  There's currently no equivalent to  
MagmaCollection, however.

The code is up on SqueakMap at  
http://map1.squeakfoundation.org/sm/package/2653845a-4738-4fa0-9e55 
-0ee596dea684 .  There's some additional information at  
http://minnow.cc.gatech.edu/squeak/3492 .

Note that it requires the latest version of GOODS (2.72) to run.

Cheers,
Avi