Python
Turbogears -- python web megaframework
restresource -- cherrypy/turbogears mixin to make it easier to expose REST resources. provides a URI convention, mapping of HTTP verbs to controller methods, and support for Accept headers
restclient -- convenience library to make it super easy to make calls to REST servers. basically wraps python's httplib in a nice way.
httplib2 -- Joe Gregario's extremely full-featured HTTP library
Twisted -- An event driven networking framework
httpy -- a sane and robust Python HTTP server library
Routes -- Routes is a Python re-implementation of the Rails routes system for mapping URL's to Controllers/Actions and generating URL's. Routes makes it easy to create pretty and concise URL's that are RESTful with little effort. The resource() functionality is particularly relevant.
Selector -- WSGI middleware for "RESTful" mapping of URL paths to WSGI applications.
wsgicollection -- Joe Gregario's wsgi middleware for handling REST resource collections
wsgi_intercept -- not directly related, but i see a lot of potential for using this to connect python+wsgi microapps directly without having to make actual, over-a-socket HTTP requests when they're both written in the same language and are deployed on the same server.
WSGIRemote -- actually allows you to do calls without over-a-socket HTTP requests, via internal WSGI requests. Also handles decoding and encoding in a somewhat symmetric manner. This is both a client and a server, though interoperable with external and non-WSGI services and clients.
mimeparse -- very useful for dealing with Accept headers
django-rest-interface -- HTTP verb dispatching and other niceties for Django.
Bourbon -- Paste + SQLAlchemy framework specifically designed for making microapps.
Ruby
http://code.whytheluckystiff.net/camping -- A ruby web microframework, built for making many small applications mounted and used together
Ruby On Rails -- The popular ruby web framework.
Simply Restful -- REST plugin for Rails
merb -- kind of a lightweight version of rails
Perl
- LWP
PHP
Java
Restlet -- Lightweight REST framework for Java
Managing/Deploying/Testing/etc
- xen
- vmware