Population-specific human leukocyte antigen (HLA) haplotype frequencies are an essential basis of

advanced algorithms for donor selection in unrelated hematopoietic stem cell transplantation. In 2016,

we introduced Hapl-o-Mat, a versatile tool for haplotype frequency estimation based on an

expectation-maximization algorithm (https://github.com/DKMS/hapl-o-Mat). Hapl-o-Mat is specifically

tailored to the analysis of HLA genes and able to cope with the heterogeneous genotyping data usually

found in donor registries. To make Hapl-o-Mat accessible to a wider range of users, we designed a graphical

user interface module that considerably facilitates the interaction with the application (https://

github.com/DKMS/hapl-o-Mat_GUI). We further provide a precompiled version of Hapl-o-Mat that can

be used on Windows personal computers without dependency on additional software libraries

(https://github.com/DKMS/hapl-o-Mat_WinBin). We are confident that these new, user-oriented features

will encourage more researchers to apply Hapl-o-Mat to their data, thereby increasing knowledge and

public availability of population-specific HLA haplotype frequencies.