From the documentation:
Adder is a Lisp-1 which compiles to Python. It aims to integrate seamlessly into Python: every Adder function is a Python function, every Adder list is a Python list, etc.
Python-on-Lisp has been tried before; I think Adder has two advantages that previous attempts did not. The first is technical: Python's metaprogramming has gotten better in the past few years, which allows Adder to integrate more smoothly. The second is social: Clojure has prepared the ground for the notion of a Lisp that integrates into an existing language.
It has one bit of non-Lispy syntax: foo.bar.baz means exactly what it does in Python, and .bar.baz is a function, defined so that (.bar.baz foo) is identical to foo.bar.baz.
Does it support tail recursion (in constant space)?
Although that would bind the function name earlier than usual for Python. In Python, you can (in theory) do this:
fact=lambda n,sofar: 3
Python wouldn't be my first choice, and I'm unconvinced that Lisp-Py makes sense, but I'm sure you'll find ways to adapt it regardless.
My main resistance is that I've used languages where you have to use special syntax for a recursive function, and I hate it. But this isn't quite the same thing.