Padify, Contentment’s flagship product, is a cloud-based system that "remixes" content for delivery across multiple tablet and smartphone devices without the need to redesign.
Men's Fitness uses Padify and has seen over 36,000 downloads since its launch at the end of 2012. The publisher plans to roll out the service to five more titles this year. Cyclist will launch its version in the next two months and Evo's will become available over the summer.
Dennis is the second investor in Contentment, alongside owner Michael Kowalski. It takes a minority share in the business, which launched last year.
Dennis Enterprise, Dennis’s entrepreneurial arm, managed the investment.
Martin Belson, managing director of Dennis Enterprise, said the decision reflected the popularity of mobile devices beyond the iPad. He said: "About a year ago it was all about the iPad, and to a lesser extent the iPhone.
"Towards the last quarter of 2012, we saw a number of major players produce high-quality tablets like the Kindle Fire and Google Nexus, and also a proliferation of smartphones in the UK market and internationally."
Dennis has been publishing digital magazines and apps since 2008 and most of its products currently use Adobe software, which requires content to be redesigned for platforms other than the iPad.
In February Dennis launched a standalone digital production agency called Adnostic, which helps advertisers produce spots across multiple platforms. Further investments are planned for the next six months.
Belson said: "We are interested in this space and we're probably a lot more advanced than other publishers. From now on it’s very much about consolidating where we are and helping these two businesses develop.
"The whole point of Dennis Enterprise is to create investment outside of our digital revenue streams. We’re not here to just be a VC and invest in start-ups: they need to have a strategic synergy with us."Follow @louiseridley