Skills inventories that people actually update
Every company has a dead skills matrix. Here is why, and what works instead.

Somewhere in your HR system is a skills matrix. It was populated in a burst of enthusiasm, it is now two years stale, and nobody trusts it enough to search it.
The failure is structural. You asked people to maintain data that benefits the company and costs them time, with no feedback loop. Of course it decayed.
Capture skills as exhaust
The reliable sources are already in the business. Project staffing records show what people actually worked on. Internal application history shows what they want next. Learning platform completions, certifications, mentoring assignments, on call rotations, code review areas. None of these require a new form.
Keep the taxonomy small and blunt
Companies drown in this. Four hundred skill tags with five levels each is a research project, not a tool. Start with thirty to fifty capabilities that map to how you actually staff work, and two levels: can do this independently, can lead others doing this.
You can refine later. You cannot recover from a taxonomy so heavy that nobody completes it.
Give people a reason to correct it
The only sustainable update mechanism is self interest. If the inventory drives which projects people get offered, which internal roles they hear about, and which training they are approved for, they will fix their own record. If it only feeds a dashboard for leadership, they will not.
Send a short prompt twice a year, prefilled with what the system inferred, asking only for corrections. Corrections are cheap. Blank forms are expensive.
Use it for planning, not scoring
The moment a skills inventory feeds into performance ratings or redundancy selection, honest data disappears. People inflate, or they hide. Keep it firmly on the opportunity side of the house and say so explicitly.
A rough inventory that is eighty percent right and refreshed quarterly is worth more than a perfect one that was true once. Aim for that and resist the urge to build the taxonomy of your dreams.