.plan

They are currently only popular among game developers to let the world know what they are working on. It was popularized by the developers at id Software and now many are using them. Many gaming web-sites are devoted to keeping track of changes and updates to these files.

Containing room for more stuff than a .project, .plans are useful for listing contact information (if you feel safe doing that). I usually list my class schedule, using the University abbreviations that are incomprehensible to anyone off-campus.

.plans were really the weblogs of the timeshare and mainframe machines. It would be where users wrote up their thoughts and theories much like today's weblogs...

Can still be seen in action at universities or other places that still have login-servers with a lot of users...