LitLaunch is a custom abstraction layer to let a mod's code run on different versions of Minecraft and in the future for other modloaders, for version-independent mods. More can be found via the LitLaunch Curseforge Page.
LitLaunch is currently in an alpha state but has support for 1.7.10, 1.8.9, 1.12.2, 1.14.4 and 1.15.2 Minecraft versions with Forge. LitLaunch also has support for Bukkit, Sponge and Spigot server environments.
Note: Meaning that the API will change over time. In the case of the TPS Mod, it is designed for a LitLaunch version will support all modloader and Minecraft versions that the LitLaunch supports.
There is also a source page that breaks down how to use LitLaunch in a development environment, deal with pull requests and more.