Some combination of [0], [1], [2], and [3] is the closest modern equivalent.

[0] https://slime.common-lisp.dev/

[1] https://github.com/joaotavora/sly

[2] https://mcclim.common-lisp.dev/

[3] https://lem-project.github.io/

Also, Portable Genera is still being developed by a former Symbolics employee but unfortunately it is only available for a chosen few, at least for now.