Java-CKKS

Relevant papers:

• Cheon, Jung Hee, et al. "Homomorphic encryption for arithmetic of approximate numbers."
• Cheon, Jung Hee, et al. "A full RNS variant of approximate homomorphic encryption."

Nice posts:

• CKKS explained series

Other (actually secure) open-source implementations:

• Microsoft SEAL
• Lattigo
• OpenFHE