Task: Card shuffles
Go: package main

import (
    "fmt"
    "math/rand"
    "time"
)

func reverse(s []int) {
    for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
        s[i], s[j] = s[j], s[i]
    }
}

func riffle(deck []int, iterations int) []int {
    le := len(deck)
    pile := make([]int, le)
    copy(pile, deck)
    for i := 0; i < iterations; i++ {
        mid := le / 2
        tenpc := mid / 10
        
        cut := mid - tenpc + rand.Intn(2*tenpc+1)
        
        deck1 := make([]int, cut)
        deck2 := make([]int, le-cut)
        copy(deck1, pile[:cut])
        copy(deck2, pile[cut:])
        pile = pile[:0]
        fromTop := rand.Intn(2) 
        for len(deck1) > 0 && len(deck2) > 0 {
            if fromTop == 1 {
                el1 := deck1[0]
                deck1 = deck1[1:]
                el2 := deck2[0]
                deck2 = deck2[1:]
                pile = append(pile, el1, el2)
            } else {
                el1 := deck1[len(deck1)-1]
                deck1 = deck1[:len(deck1)-1]
                el2 := deck2[len(deck2)-1]
                deck2 = deck2[:len(deck2)-1]
                pile = append(pile, el1, el2)
            }
        }
        
        if len(deck1) > 0 {
            pile = append(pile, deck1...)
        } else if len(deck2) > 0 {
            pile = append(pile, deck2...)
        }
        reverse(pile) 
    }
    return pile
}

func overhand(deck []int, iterations int) []int {
    le := len(deck)
    pile := make([]int, le)
    copy(pile, deck)
    pile2 := make([]int, 0)
    twentypc := le / 5
    for i := 0; i < iterations; i++ {
        for len(pile) > 0 {
            cards := 1 + rand.Intn(twentypc)
            if cards > len(pile) {
                cards = len(pile)
            }
            temp := make([]int, cards)
            copy(temp, pile[:cards])
            pile2 = append(temp, pile2...)
            pile = pile[cards:]
        }
        pile = append(pile, pile2...)
        pile2 = pile2[:0]
    }
    return pile
}

func main() {
    rand.Seed(time.Now().UnixNano())
    fmt.Println("Starting deck:")
    deck := make([]int, 20)
    for i := 0; i < 20; i++ {
        deck[i] = i + 1
    }
    fmt.Println(deck)
    const iterations = 10
    fmt.Println("\nRiffle shuffle with", iterations, "iterations:")
    fmt.Println(riffle(deck, iterations))
    fmt.Println("\nOverhand shuffle with", iterations, "iterations:")
    fmt.Println(overhand(deck, iterations))
    fmt.Println("\nStandard library shuffle with 1 iteration:")
    rand.Shuffle(len(deck), func(i, j int) {
        deck[i], deck[j] = deck[j], deck[i] 
    })
    fmt.Println(deck)
}

VB: Imports System.Runtime.CompilerServices
Imports System.Text

Module Module1

    <Extension()>
    Function AsString(Of T)(c As ICollection(Of T)) As String
        Dim sb = New StringBuilder("[")
        sb.Append(String.Join(", ", c))
        Return sb.Append("]").ToString()
    End Function

    Private rand As New Random()

    Function RiffleShuffle(Of T)(list As ICollection(Of T), flips As Integer) As List(Of T)
        Dim newList As New List(Of T)(list)

        For n = 1 To flips
            
            Dim cutPoint As Integer = newList.Count / 2 + If(rand.Next(0, 2) = 0, -1, 1) * rand.Next(newList.Count * 0.1)

            
            Dim left As New List(Of T)(newList.Take(cutPoint))
            Dim right As New List(Of T)(newList.Skip(cutPoint))

            newList.Clear()

            While left.Count > 0 AndAlso right.Count > 0
                
                
                
                If rand.NextDouble() >= left.Count / right.Count / 2 Then
                    newList.Add(right.First())
                    right.RemoveAt(0)
                Else
                    newList.Add(left.First())
                    left.RemoveAt(0)
                End If
            End While

            
            If left.Count > 0 Then
                newList.AddRange(left)
            End If
            If right.Count > 0 Then
                newList.AddRange(right)
            End If
        Next

        Return newList
    End Function

    Function OverhandShuffle(Of T)(list As ICollection(Of T), passes As Integer) As List(Of T)
        Dim mainHand As New List(Of T)(list)

        For n = 1 To passes
            Dim otherhand = New List(Of T)

            While mainHand.Count > 0
                
                Dim cutSize = rand.Next(list.Count * 0.2) + 1

                Dim temp = New List(Of T)

                
                Dim i = 0
                While i < cutSize AndAlso mainHand.Count > 0
                    temp.Add(mainHand.First())
                    mainHand.RemoveAt(0)
                    i = i + 1
                End While

                
                If rand.NextDouble() >= 0.1 Then
                    
                    temp.AddRange(otherhand)
                    otherhand = temp
                Else
                    
                    otherhand.AddRange(temp)
                End If
            End While

            
            mainHand = otherhand
        Next

        Return mainHand
    End Function

    Sub Main()
        Dim list = New List(Of Integer)(Enumerable.Range(1, 20))
        Console.WriteLine(list.AsString())
        list = RiffleShuffle(list, 10)
        Console.WriteLine(list.AsString())
        Console.WriteLine()

        list = New List(Of Integer)(Enumerable.Range(1, 20))
        Console.WriteLine(list.AsString())
        list = RiffleShuffle(list, 1)
        Console.WriteLine(list.AsString())
        Console.WriteLine()

        list = New List(Of Integer)(Enumerable.Range(1, 20))
        Console.WriteLine(list.AsString())
        list = OverhandShuffle(list, 10)
        Console.WriteLine(list.AsString())
        Console.WriteLine()

        list = New List(Of Integer)(Enumerable.Range(1, 20))
        Console.WriteLine(list.AsString())
        list = OverhandShuffle(list, 1)
        Console.WriteLine(list.AsString())
        Console.WriteLine()
    End Sub

End Module