I've just finished reading Clannad. While I was browsing for another visual novel to read, I saw the Tomoyo After (after story of Tomoyo's route) visual novel.
Now I'm wondering whether maybe the other heroines also have an after story but they have different titles.
Tomoyo is the only one who has a separate visual novel.
In general, whenever you have questions about how visual novels are interrelated, a good first stop is the VN's relationship diagram on VNDB - here's the one for Clannad.
You'll notice in this case that there appear to be other related VNs like "Kyou After" and "Clannad: Lost Winter", but note that those are indicated by dotted arrows on the diagram. This indicates that the relationship is "unofficial", which typically means that one of the two things linked by the arrow is a fan-produced work.