diff --git a/src/ManyArrayList.zig b/src/ManyArrayList.zig
new file mode 100644
index 0000000000000000000000000000000000000000..4e88d404ebc252c45694ac9de6494ca5061a6445
--- /dev/null
+++ b/src/ManyArrayList.zig
@@ -0,0 +1,102 @@
+const std = @import("std");
+const extras = @import("./lib.zig");
+
+pub fn ManyArrayList(T: type) type {
+    return struct {
+        allocator: std.mem.Allocator,
+        list: std.ArrayListUnmanaged(T),
+        lengths: std.ArrayListUnmanaged(usize),
+
+        pub fn init(allocator: std.mem.Allocator) @This() {
+            return .{
+                .allocator = allocator,
+                .list = .{},
+                .lengths = .{},
+            };
+        }
+
+        pub fn deinit(self: *@This()) void {
+            self.list.deinit(self.allocator);
+            self.lengths.deinit(self.allocator);
+        }
+
+        pub fn add(self: *@This()) !usize {
+            const n = self.lengths.items.len;
+            try self.lengths.append(self.allocator, 0);
+            return n;
+        }
+
+        pub fn appendSlice(self: *@This(), n: usize, slice: []const T) !void {
+            const real_n = extras.sum(usize, self.lengths.items[0 .. n + 1]);
+            try self.list.insertSlice(self.allocator, real_n, slice);
+            self.lengths.items[n] += slice.len;
+        }
+
+        pub fn items(self: *@This(), n: usize) []T {
+            const real_n = extras.sum(usize, self.lengths.items[0..n]);
+            const len = self.lengths.items[n];
+            return self.list.items[real_n..][0..len];
+        }
+
+        pub fn set(self: *@This(), n: usize, slice: []const T) !void {
+            const real_n = extras.sum(usize, self.lengths.items[0..n]);
+            try self.list.replaceRange(self.allocator, real_n, self.lengths.items[n], slice);
+            self.lengths.items[n] = slice.len;
+        }
+
+        pub fn clear(self: *@This(), n: usize) void {
+            const real_n = extras.sum(usize, self.lengths.items[0..n]);
+            self.list.replaceRangeAssumeCapacity(real_n, self.lengths.items[n], &.{});
+            self.lengths.items[n] = 0;
+        }
+
+        /// Does not reset .lengths so that deinit can still clean it up
+        pub fn toOwnedSlice(self: *@This()) ![]T {
+            return self.list.toOwnedSlice(self.allocator);
+        }
+
+        pub fn swap(self: *@This(), a: usize, b: usize) void {
+            std.debug.assert(a != b);
+            if (a < b) return self.swapLR(a, b);
+            if (a > b) return self.swapLR(b, a);
+            unreachable;
+        }
+        fn swapLR(self: *@This(), a: usize, b: usize) void {
+            extras.swapManyLR(
+                u8,
+                self.list.items,
+                extras.sum(usize, self.lengths.items[0..a]),
+                self.lengths.items[a],
+                extras.sum(usize, self.lengths.items[0..b]),
+                self.lengths.items[b],
+            );
+            std.mem.swap(
+                usize,
+                &self.lengths.items[a],
+                &self.lengths.items[b],
+            );
+        }
+
+        pub fn remove(self: *@This(), n: usize) void {
+            const real_n = extras.sum(usize, self.lengths.items[0..n]);
+            self.list.replaceRangeAssumeCapacity(real_n, self.lengths.items[n], &.{});
+            _ = self.lengths.orderedRemove(n);
+        }
+
+        pub fn replace(self: *@This(), n: usize, o: usize, l: usize, slice: []const T) !void {
+            std.debug.assert(o + l <= self.lengths.items[n]);
+            const real_n = extras.sum(usize, self.lengths.items[0..n]);
+            try self.list.replaceRange(self.allocator, real_n + o, l, slice);
+            self.lengths.items[n] -= l;
+            self.lengths.items[n] += slice.len;
+        }
+
+        pub fn insertAt(self: *@This(), n: usize, slice: []const T) !void {
+            try self.lengths.ensureUnusedCapacity(self.allocator, 1);
+            try self.list.ensureUnusedCapacity(self.allocator, slice.len);
+            const real_n = extras.sum(usize, self.lengths.items[0..n]);
+            self.lengths.insertAssumeCapacity(n, slice.len);
+            self.list.insertSlice(self.allocator, real_n, slice) catch unreachable;
+        }
+    };
+}
diff --git a/src/lib.zig b/src/lib.zig
index bc88c45e19bde5bfb50c8a2586d48c75f4bb4d6c..06ae72cba17f704546f16aa2554178d6f0b0c629 100644
--- a/src/lib.zig
+++ b/src/lib.zig
@@ -113,3 +113,4 @@ pub usingnamespace @import("./StaticMultiList.zig");
 pub usingnamespace @import("./join.zig");
 pub usingnamespace @import("./omit.zig");
 pub usingnamespace @import("./swapMany.zig");
+pub usingnamespace @import("./ManyArrayList.zig");