CAS Calc is free and simple app which can perform many functions of the TI-Nspire.

Features:
-Scientific Calculator: Line-By-Line with Variables Support
-Loop Calculation: Quickly Evaluate For Multiple Values

Numbers:
-Convert Decimal to Fraction
-Factor a Number
-Calculate Least Common Multiple
-Calculate Greatest Common Denominator
-Calculate Remainder
-Convert to Proper Fraction

Algebra:
-Solve for a Variable
-Factor an Expression
-Expand an Expression
-Divide Polynomials

Calculus:
-Differentiate (Find Derivative)
-Integrate (Find Integral)
-Calculate Limit
-Calculate Sum
-Calculate Product
-Find Tangent Line
-Find Normal Line

Probability:
-Evaluate Factorial
-Calculate Permutations
-Calculate Combinations

Statistics:
-Calculate Arithmetic Mean
-Find Median
-Find Minimum
-Find Maximum
-Calculate Sample Standard Deviation
-Calculate Sample Variance
-Calculate Population Standard Deviation
-Calculate Population Variance