V12 Data - V12 Data offers rich data sets with verified addresses and emails for personalized marketing campaigns.
Radius Networks - Radius Networks offers mobile proximity technologies.
Lotame - Make your data actionable, learn about your most valuable customers, improve ROI by targeting the right audience and increase relevance across screens.
ROXIMITY - ROXIMITY is a mobile advertising platform that enables retailers and brands to send targeted, location-based messaging to nearby customers.
Google Audience Center - 3 votes and 6 comments so far on Reddit
AltBeacon - AltBeacon is an open and interoperable specification for proximity beacons.