Founded in 2015, Yapster has developed an instant messaging protocol for front-of-house retail teams.
Customers using the app include BrewDog, a UK-based brewery and pub chain, as well as coffee house Caffè Nero and UK highway service station operator Welcome Break.
In addition to the core offer, Yapster's platform also enables employee learning, labour management and rewards.
Sona's platform already lets users launch instant messaging chats as part of its workforce management suite, which also includes scheduling, attendance and absence management.
However buying Yapster should aid its UK expansion, particularly given overall strength in the HR software space.
More employers are seeking efficiencies by hopping on the digitisation gravy train. Yesterday Tech.eu reported on a HR software deal in Germany, specifically in the commercial cleaning services sector.
VC funding to Sona has totalled over $10 million to date from investors including Gradient Ventures, Google's AI-focused venture fund.
Rob Liddiard, co-founder and CEO of Yapster, said: "All companies are under pressure to accomplish more with less right now, which means doing everything possible to get the most out of employees.
"Sona, with its backing from Gradient Ventures, is the only technology supplier I’ve seen in my 7 years running Yapster that appears truly capable of delivering the consumer-grade design and AI power customers are now crying out for in order to solve their productivity puzzles."
Steffen Wulff Petersen, CEO and co-founder of Sona, added: "Yapster and its team are widely respected across the retail sector, and we see extraordinary potential to accelerate Sona’s mission with this acquisition of their expertise.
"Employees today expect company software to be as powerful and easy to use as their favourite personal apps - and that’s precisely the level of customer experience Sona was founded on and funded to deliver.”