Google Transit Feed Specification.
Not a link, but a protocol that can be used to display real or static time that's open sourced so any developer can incorporate it into their app.
NYCT's feed is Quad-tier (static, real time, service alert, variable) which is the most detail.
The Bee Line GTFS, by comparison, is only single tier (static), and NICE is tri-tier (real, static, and variable).