If you've been invited by the person who initiated this near you, you'll have access and the ability to edit the rows of the spreadsheet feeding data to this site.
Simply add the rows for the tools you have and add yes if an item is currently being borrowed. Easy, the Spreadsheet auto-saves, too!
More details for using this project here.
The site is open source (free for all), uses a Google Spreadsheet for the data and is designed to be duplicated and live in minutes (Fork-n-go!). You can set up your own by following the instructions attached to the project's code on GitHub. GitHub also hosts these pages for free with GitHub Pages.
Built by @jllord.