HLN participates actively in a number of open source software development projects, including:

The Immunization Calculation Engine (ICE) is a service-oriented, standards-based immunization forecasting software system that evaluates a patient's immunization history and also generates the appropriate immunization recommendations for the patient. ICE can be deployed in diverse technical environments and is designed to easily integrate with third party clinical systems through its standards-based Web Service. The ICE software distribution also includes two GUI tools that enable subject matter experts to manage the immunization algorithm and to manage and execute a set of fully automated tests, all without the intervention of software developers. ICE is currently being integrated with two separate Immunization Information Systems (IIS) and a leading Electronic Health Record System (EHR-S). The ICE software system, including the supporting tools, does not depend on any commercial software and will be publicly released under an open source license before the end of 2012. ICE has been implemented as a clinical module within OpenCDS, a software framework that provides developers with a set of standards-based clinical decision support (CDS) resources designed to enable CDS at scale.

Choicemaker Technology, an open source release of record-matching software developed by ChoiceMaker Technologies, Inc. While not developing the core software, HLN works closely to integrate this technology into public health systems including New York City's Citywide Immunization Registry. Choicemaker software "mimics" human intuition by comparing two records, testing a set of conditions in the data (which it calls "clues"), and develops a probability score that the two records are for the same person. Different clues receive different weights by the model designers in conjunction with a software-assisted "training" process whereby through machine learning the Choicemaker software "learns" the optimum weights based on normative data supplied to the algorithm.

HLN has been integrating this technology into MPI solutions as part of its overall interest in person data de-duplication strategies. In NYC, HLN created a sophisticated set of services — initially using OMG's CORBA and later with Web Services — to allow systems to use the Choicemaker model.