Support for an Excel "Add-In" called EIRT was added in July 2015.  This add-in was initially created in 2006 and has been updated regularly since then by its three authors.  EIRT has been available on "Source Forge" for some time, where equivalent IRT routines for use with the R language are found in a package called RIRT .


Here's a description from EIRT's Readme.doc file:


This add-in for Excel provide a 'wizard' to estimates the items and

latent variables from the responses of subjects to a

questionnaire. The supported dichotomous IRT (Item Response

Theory) models are the 1PLM (one parameter logistic model), the

2PLM (two parameter logistic model) and the 3PLM (three

parameter logistic model). For polytomous items, Bock's nominal

model, and Samejima's graded model are supported. Two

nonparametric methods (kernel regression an PMMLE) are also

supported.  The estimations methods available are the MMLE

(marginal maximum likelihood estimator) and the BME (Bayes

modal estimator, for dichotomous models only) for the

parametric estimation of items, the PMMLE (Penalized MMLE) and

the kernel regression (Nadaraya-Watson) for the nonparametric

estimation of items, and the EAP (expectation a posteriori) and

WMLE (Warm's maximum likelihood estimator) for the latent

variable predictions.


From the description, you might sense that English is not the native language of the authors (in fact it's French).  You'll get the same impression when running EIRT, but you shouldn't be put off -- EIRT blends in nicely with Lertap 5, and has power.


Read much more about it in this document.