IPA-CuCl3
By definition people usually assume antiferromagnetic interactions when talking about the spin ladders. IPA-CuCl3 is an interesting exception, as it features ferromagnetic interaction on the rung. Thus, two copper spins-1/2 are forming an effective S=1 object, and overall ladder becomes equivalent to a Haldane chain. It is also gapped, but the mechanism for gap generation is completely different.
In addition, IPA-CuCl3 is somewhat frustrated (as there are some "diagonal" interactions). And finally, it also allows for the replacement of chlorine by bromine - a substitution that creates disorder in Heisenberg exchange bonds. Accessible energy scale thus allows to fully study the impact of such disorder on properties of 1D magnet in both gapped and gapless phases.
B. Náfrádi, T. Keller, H. Manaka, A. Zheludev, and B. Keimer, Low-Temperature Dynamics of Magnons in a Spin-1/2 Ladder Compound, external pagePhys. Rev. Lett. 106, 177202 (2011)
B. Nafradi, T. Keller, H. Manaka, U. Stuhr, A. Zheludev, B. Keimer, Bond Randomness Induced Magnon Decoherence in a Spin-1/2 Ladder Compound, external pagePhys. Rev. B 87, 020408(R) (2013); external pagearXiv:1211.4741
G. S. Perren, W. E. A. Lorenz, E. Ressouche, and A. Zheludev, Field-induced ordering in a random-bond quantum spin ladder compound with weak anisotropy, external pagePhys. Rev. B 97, 174431 (2018).