The R-package metacart is available here.
When you use metacart please refer to: Li, X., Dusseldorp, E., & Meulman, J. J. (2017). Meta-CART: A tool to identify interactions between moderators in meta?analysis. British Journal of Mathematical and Statistical Psychology, 70(1), 118-136.

The R-package stima (simultaneous threshold interaction modelling algorithm) is available on request by sending an e-mail to me.
When you use stima, please refer to:
Dusseldorp, E., Conversano, C., & Van Os, B.J. (2010). Combining an additive and tree-based regression model simultaneously: STIMA. Journal of Computational and Graphical and Statistics, 19 (3), 514-530.

The R-package quint (qualitative interaction trees) is available here.
When you use quint, please refer to:
Dusseldorp, E., & Van Mechelen, I. (2014). Qualitative interaction trees: a tool to identify qualitative treatment-subgroup interactions. Statistics in medicine, 33(2), 219-237.

Both packages are suitable for R version 3.0.2 and higher. More information about the R Software environment can be found here