The tar file package toy.tar.Z contains the following toy codes
for unperturbed two-body motion (page references are to the book
Gravitational N-Body Simulations):

BASIC   Standard Hermite (p.27 and 374).

KSREG   KS difference method (p.18 and 56).

HERMIT  Hermite KS (p.62).

STUMPF  Stumpff KS method (p.63 and 186).

TAYLOR  Taylor KS with c-functions (p.63).

BHREG   Burdet-Heggie method (p.60).

All the five regularization codes are constructed in the same
way, with calls to relevant N-body routines suppressed. They
are also made to look very similar to some of the large codes
on which they are based. This design therefore serves as an
introduction to realistic N-body codes of different complexity.
At the same time, the treatment of just one binary makes the
implementation very simple. Finally, note that the above codes
employ methods which either have been used or are appropriate
for large simulations.

Cambridge 17/3/04
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A new version of the KS toy code HERMIT includes Post-Newtonian
terms based on Mora & Wills (gr-qc/0312082 v3 of May 2005).
Subroutine KSREL includes the perturbing force as well as the
first derivative, derived by Pau Amaro-Seoane. The optional
alternative GRPERT only includes the perturbing force. The code
in hermit.tar.Z can be used to explore GR effects in binaries.
It is identical to the original if speed of light is zero.
SJA 14/6/06

The version ksreg2.tar.gz contains a Hermite toy code with PN2.5 and
derivative terms. The radiation energy loss is also integrated to
high accuracy using a 4th-order formulation due to Keigo Nitadori 2012.
SJA/ 1/10/2012