I heartily endorse this product. JUICE eats Chisel's lunch, then the lunch it brought for itself from home, then some cookies from the vending machine. It's that good.
JUICE is a Java-based--and, therefore, cross-platform--utility for editing map files. It can't replace a dedicated editor like Forge, but it is capable of editing several aspects of map files, most of which are geared toward fixing and tweaking network maps. For example, you can edit existing and place new level objects; you can change monster and item parameters; you can do some things that no other editor will let you do. If you're a mapmaker who needs to edit these sorts of things, but without consistent access to a Macintosh, give JUICE a try.
A manual is included, both in HTML and PDF forms.
v1.1.1 adds the ability to embed shapes patches.
v1.1 includes the long-anticipated texture converter.