Every application rationalisation starts with one thing: knowing what you actually have. A good application inventory is the foundation everything else is built on.

You can't score, classify or rationalise applications you can't see. The inventory turns a vague sense of "we have too many systems" into a concrete, workable list.
Pull from finance (what you pay for), IT asset and identity systems (what's deployed and who uses it), and business owners (what it's for and how important it is). Expect gaps — the goal is "good enough to decide", not perfection.
An inventory is only useful if it feeds decisions. Structure it so it flows straight into scoring and TIME classification, rather than becoming a static list that ages on a shared drive.
The Applications Assessment & Rationalisation Toolkit includes a data-collection template that feeds straight into the scoring calculator and TIME quadrant.