It is a great onboard environment for development just on the Palm. You can use it either in a simple REP (Read - Evaluate - Print) loop style or compile and run apps with a user interface. It uses a runtime file on the device as support.
Source is stored in memos or doc documents.
It includes simple Palm extensions to allow you to do most useful things:
Home page, with older Plua 1.1 version http://meusite.uai.com.br/~mmand/plua/plua.htm
Active Yahoo Group at http://groups.yahoo.com/group/plua/ including some sample files and latest beta (essential for Tungsten and other later Palms).
I started these Plua wiki pages because I am accustomed to using a Wiki and wanted to make it easier to capture some of the better discussions rather than searching the mailing list archives.
DEFINITELY join the Yahoo group if you have any interest in Plua -- the site doesn't appear to be getting regular maintenance, and some of the links have died.
Plua v1.1 has TCP networking support, sort of -- it works well enough for batch-style purposes (HTTP, for example) but seems to have problems which get in the way of real full-duplex interactivity. Still, it's a million times better than nothing.
-- Aaron 2005-12-20
Plua 2.0 is very advanced now but only available from the Yahoo group : http://groups.yahoo.com/group/plua/
-- SD 2006-10-20
Another free software for Palm find at http://www.palm-freeware.org/