Suggestions for Default

The following packages have something in common with the package Default. The packages are ordered in decreasing similarity.

Package eoldef: Define commands which absorb the whole source line as arguments
Package advice: Extend commands and environments
Package defstring: Define macros as verbatim macros
Package namedef: TeX definitions with named parameters
Package lparse: Parse macro arguments with Lua using xparse-like specification
Package hitex-def: Support files for HiTeX
Package balancedquotes: Code balanced quotes according to document language
Package compare: Macro to compare two strings
Package patch: Modify already-loaded packages
Package styledcmd: Handling multiple versions of user-defined macros
Package ccool: A key-value document command parser
Package getoptk: Define macros with sophisticated options
Package ltxnew: A simple means of creating commands
Package xoptarg: Expandable macros that take an optional argument
Package xnewcommand: Define \global and \protected commands with \newcommand
Package optparams: Macros with multiple optional parameters
Package laps: Zero-width boxes for annotations, etc.
Package tokcycle: Build tools to process tokens from an input stream
Package cdcmd: Expandable conditional commands for LaTeX
Package lambdax: Use Lambda expression within LaTeX
Package mathcommand: \newcommand-like commands for defining math macros
Package xfp: Interface to the LaTeX3 floating point unit
Package xparse: A generic document command parser
Package inlinedef: Inline expansions within definitions
Package cssyntax: Readable, self-documenting command names for LaTeX package authors
Package xtemplate: A high-level interface for declaring document commands
Package letltxmacro: Let assignment for LaTeX macros
Package causalmodels: Notation macros for causal graphical models
Package collargs: Collect arguments of any command
Package localloc: Macros for localizing TeX register allocations
Package tokmap: Iterate over a token list expandably, without dropping spaces or braced groups