Included in the set are Gravitation, the two-player Between, and Rohrer's best-known game Passage, which is also available on iPhone. This DS collection, then, will be another option for those who want to feel terrible about their mortality on the go.
Sabarasa's recent press releases list the Alt-Play collection as an "upcoming project," and confirm that it's being made for the DSiWare platform. It certainly makes sense as a download: it may be three games, but those are three very brief games.
[Update: Sabarasa press releases also mention that Rohrer's puzzle game Primrose will be released separately on DSiWare.]