Psi4 can provide CC3 ground- and excited-state energies for open-shell systems, but not if you require spin-adapted triplets. The RHF-CC3 code is limited to closed-shell singlets, but, if you’re not too concerned about the exact spin state, the UHF-CC3 code may work for you.
The memory requirements are actually similar to the CCSD code’s requirements because the triples are handled in a batched way to avoid storage of the full list of amplitudes. The UHF-CC3 codes isn’t as well optimized in terms of either memory or CPU as the RHF-CC3 code, but it might still work.