Wikipedia
Mxparser
mXparser is an open-source mathematical expressions parser/evaluator providing abilities to calculate various expressions at a run time. Expressions definitions are given as plain text, then verified in terms of grammar / syntax, finally calculated. Library source code is maintained separately for Java and C#, providing the same API for Java/JVM, Android, .NET and MONO ( Common Language Specification Compliant). Software is free and is distributed under Simplified BSD License.