diff --git a/pkg/app/server/unregisteredappstore/BUILD.bazel b/pkg/app/server/unregisteredappstore/BUILD.bazel
new file mode 100644
index 0000000000..c1ca8d6cb5
--- /dev/null
+++ b/pkg/app/server/unregisteredappstore/BUILD.bazel
@@ -0,0 +1,15 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["store.go"],
+    importpath = "github.com/pipe-cd/pipecd/pkg/app/server/unregisteredappstore",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/cache:go_default_library",
+        "//pkg/cache/rediscache:go_default_library",
+        "//pkg/model:go_default_library",
+        "//pkg/redis:go_default_library",
+        "@org_uber_go_zap//:go_default_library",
+    ],
+)
diff --git a/pkg/app/server/unregisteredappstore/store.go b/pkg/app/server/unregisteredappstore/store.go
new file mode 100644
index 0000000000..2bd0846cd1
--- /dev/null
+++ b/pkg/app/server/unregisteredappstore/store.go
@@ -0,0 +1,104 @@
+// Copyright 2022 The PipeCD Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package unregisteredappstore
+
+import (
+	"bytes"
+	"context"
+	"encoding/gob"
+	"errors"
+	"fmt"
+
+	"go.uber.org/zap"
+
+	"github.com/pipe-cd/pipecd/pkg/cache"
+	"github.com/pipe-cd/pipecd/pkg/cache/rediscache"
+	"github.com/pipe-cd/pipecd/pkg/model"
+	"github.com/pipe-cd/pipecd/pkg/redis"
+)
+
+type Store interface {
+	ListApplications(ctx context.Context, projectID string) ([]*model.ApplicationInfo, error)
+	PutApplications(projectID, pipedID string, apps []*model.ApplicationInfo) error
+}
+
+type store struct {
+	backend redis.Redis
+	logger  *zap.Logger
+}
+
+func NewStore(r redis.Redis, logger *zap.Logger) Store {
+	return &store{
+		backend: r,
+		logger:  logger,
+	}
+}
+
+func (c *store) ListApplications(_ context.Context, projectID string) ([]*model.ApplicationInfo, error) {
+	key := makeUnregisteredAppsCacheKey(projectID)
+	hc := rediscache.NewHashCache(c.backend, key)
+
+	// pipedToApps assumes to be a map["piped-id"][]byte(slice of *model.ApplicationInfo encoded by encoding/gob)
+	pipedToApps, err := hc.GetAll()
+	if errors.Is(err, cache.ErrNotFound) {
+		return []*model.ApplicationInfo{}, nil
+	}
+
+	if err != nil {
+		c.logger.Error("failed to get unregistered apps", zap.Error(err))
+		return nil, err
+	}
+
+	// Integrate all apps cached for each Piped.
+	allApps := make([]*model.ApplicationInfo, 0)
+	for _, as := range pipedToApps {
+		b, ok := as.([]byte)
+		if !ok {
+			return nil, errors.New("unexpected data cached")
+		}
+
+		dec := gob.NewDecoder(bytes.NewReader(b))
+		var apps []*model.ApplicationInfo
+		if err := dec.Decode(&apps); err != nil {
+			c.logger.Error("failed to decode the unregistered apps", zap.Error(err))
+			return nil, err
+		}
+
+		allApps = append(allApps, apps...)
+	}
+
+	return allApps, nil
+}
+
+func (c *store) PutApplications(projectID, pipedID string, apps []*model.ApplicationInfo) error {
+	var buf bytes.Buffer
+	enc := gob.NewEncoder(&buf)
+	if err := enc.Encode(apps); err != nil {
+		c.logger.Error("failed to encode the unregistered apps", zap.Error(err))
+		return err
+	}
+
+	key := makeUnregisteredAppsCacheKey(projectID)
+	hc := rediscache.NewHashCache(c.backend, key)
+	if err := hc.Put(pipedID, buf.Bytes()); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func makeUnregisteredAppsCacheKey(projectID string) string {
+	return fmt.Sprintf("HASHKEY:UNREGISTERED_APPS:%s", projectID)
+}