It has been remarked on that the current category system is mildly non-specific for Minecraft Mods. So we gave you new specific categories that should help better organize your mods and help end users find what they are looking for.
When editing categories, make sure you change both Primary and Secondary categories. Use Project Management and click on Edit Project. Then go down and use the dropdown menu to select your Primary Category then pick up to 4 Secondary Categories.
The old categories have been moved to Legacy and will be disappearing when the new system is put in place. Currently if you are using a Legacy Category other than Forge or Other users will not be able to sort with that category.
Feel free to comment if you feel a category is missing.