The basics:

1t1d stands for "One Thing One Day". It is a recurring project held by Transtagonist.

The details:

For each project, the creator makes one "thing" of a specific type for each day of a predetermined period of time. A "thing" can be anything: a drawing, a short film, a birdhouse, a story, etc. The period of time is also open-ended, though two weeks is a typical time.

Other special rules can be applied to a project. For example, before starting, a phrase is often assigned to each day for inspiration.

The purpose:

An artist or craftsman often needs guidance, challenge, and inspiration. Working within limitations can be both restrictive and helpful. Unusual limitations like short production time make a creator need to work faster, and often make him|r think in a different way.

That said, 1t1d ends up being about whatever the creator makes it, but there is usually a focus on quantity of output, as well as routine.