This is the US only index of the MIT Billion Prices Project.
This index uses prices for online goods. From MIT:
These indexes are designed to provide real-time information on major inflation trends, not to forecast official inflation announcements. We are constantly adding new categories of goods, but we do not cover 100% of CPI goods and services. The price of services, in particular, are not easy to find online and therefore are not included in our statistics.
It appears that year-over-year inflation is around 1.5%.
The recent monthly decline is probably related to oil and gasoline prices, but this is another measure that suggests inflation is not currently a problem.