In WeEstimate, you can look at the list of Parts on the WeEstimate database by going to Tools -> Parts Editors.
If you are looking to get a list of all Manufacturers in the system you need to:
1. Go to Tools
2. Click on Parts Editors
3. Under the Search field type "%%%" to find for all parts in the system. Depending on the number of parts on your database this might take a few seconds.
4. Drag the Manufacturer field to group by it. (This can be done with any column)