Any games that were or still are considered vaporware. Usually requires that news about the game pop up repeatedly over several (3-5+) years but nothing tangible appearing.
Alternate names: Development hell, Development limbo
The first video game about Vaporware was released in 1990.
Rumors with sufficient evidence, if they keep popping up for say 3-5 years would qualify in some cases (if limited to preproduction planning, renders, and concept art then maybe not, actual in-game content however would). Official announcement and then no release for 1-3 years would also qualify.