  A wide range of astrophysical sources exhibit extreme and rapidly varying
electromagnetic emission indicative of efficient non-thermal particle
acceleration. Understanding these sources often involves comparing data with a
broad range of theoretical scenarios. To this end, it is beneficial to have
tools that enable not only fast and efficient parametric investigation of the
predictions of a specific scenario but also the flexibility to explore
different theoretical ideas. In this paper, we introduce \texttt{Tleco}, a
versatile and lightweight toolkit for developing numerical models of
relativistic outflows, including their particle acceleration mechanisms and
resultant electromagnetic signature. Built on the Rust programming language and
wrapped into a Python library, \texttt{Tleco} offers efficient algorithms for
evolving relativistic particle distributions and for solving the resulting
emissions in a customizable fashion. \texttt{Tleco} uses a fully implicit
discretization algorithm to solve the Fokker-Planck (FP) equation with
user-defined diffusion, advection, cooling, injection, and escape, and offers
prescriptions for radiative emission and cooling. These include, but are not
limited to, synchrotron, inverse-Compton, and self-synchrotron absorption.
\texttt{Tleco} is designed to be user-friendly and adaptable to model particle
acceleration and the resulting electromagnetic spectrum and temporal
variability in a wide variety of astrophysical scenarios, including, but not
limited to, gamma-ray bursts, pulsar wind nebulae, and jets from active
galactic nuclei. In this work, we outline the core algorithms and proceed to
evaluate and demonstrate their effectiveness. The code is open-source and
available in the GitHub repository: \href{https://github.com/zkdavis/Tleco
