Options that I see:
- programming works, but it's too vague. It's also very similar to the name of the site. It also covers a lot of ground and could be put on a lot of questions here.
- construction exists, but has been used to refer to constructors. Construction is the phase name as defined in the SWEBOK. However, the SWEBOK definition for "construction" includes coding, verification, unit testing, and integration testing.
- coding seems simplistic to me, but it exists with 66 questions tagged. It seems like this is the current standard, although I've seen questions about the act of writing code not tagged with it.
- implementation exists in a plural form implementations. However, this tag refers to implementations of features, usually at the language level (from what I gathered). Having two very similar tags to refer to two very different things seems silly and confusing.
It looks like coding is the winner, but I'm not sure if it's the best choice. It works, it's well understood, and it has some meaning. What does the community think, though?