Addon company = Allows you to have more than one company on the same installation, so you can have companya.com and companyb.com with one installation to update and log into but the staff who have access to one won't know there's two unless you give them permission to both. See: http://videos.blesta.com/video/65308950
License Manager Addon = Allows you to resell licenses for your products like Phillips Data does they license their software Blesta and they use the license manager to do it for them. We sell a BlestaCMS Plugin which we license so we use the license manager to license that plugin, etc. Sadly no video for that but you can see the docs here:
- Module for making products: https://docs.blesta.com/display/user/License+Module
- Plugin for callling home: https://docs.blesta.com/display/user/License+Manager