Reaper

A lightweight macOS menu bar app for monitoring and killing processes. Like Activity Monitor, but faster.

Features

• Process grouping -- Apps and their helper processes are grouped together by walking the parent PID chain and matching bundle ID prefixes. Expand any group to see individual helpers.
• One-click kill -- Hover to reveal a quit button. Right-click for force quit (SIGKILL). Kill an entire process group at once.
• 9 menu bar indicator styles -- Pill bar, segments, thin line, ring gauge, battery, dots, mini bars (history graph), dual stack (CPU + memory), and text only.
• Per-metric indicator style -- Set a different visual style for CPU vs. memory. Each metric remembers its own default.
• Hide text option -- Strip the percentage/memory label from the menu bar for a minimal footprint. The indicator graphic remains.
• Global hotkey -- Toggle the panel with a keyboard shortcut. Default is Control+Option+Command+R, configurable via an inline recorder using the KeyboardShortcuts library.
• Search and sort -- Filter processes by name. Sort by CPU, memory, or name. Groups and their children are both sorted.
• Paginated background processes -- The "Background" catch-all group paginates children 10 at a time with a "Show more" button.
• Auto-expand on search -- When a search query is active, matching helper processes are shown automatically without needing to expand the group.
• Settings -- Configurable refresh interval (1s, 2s, 3s, 5s), launch at login via SMAppService.

Install

Homebrew

brew install --cask nclandrei/tap/reaper

Manual

Download the latest .dmg from Releases and drag Reaper to Applications.

Build from Source

Requires XcodeGen and Xcode 15+.

brew install xcodegen
cd reaper
xcodegen generate
xcodebuild build \
  -project Reaper.xcodeproj \
  -scheme Reaper \
  -configuration Release

The built app will be in DerivedData. To run directly:

open DerivedData/Reaper/Build/Products/Release/Reaper.app

Architecture

MVVM with a service layer, built entirely in SwiftUI.

Layer	Components
Models	ProcessInfo, ProcessGroup, SortOrder, MenuBarStyle, MenuBarMetric
Services	ProcessMonitor (sysctl + proc_pidinfo), ProcessKiller (SIGTERM/SIGKILL), SystemStats (Mach host_statistics)
ViewModels	ProcessListViewModel (timer, grouping, search, sort), SettingsViewModel (refresh interval, launch at login)
Views	NSPopover-hosted SwiftUI tree, custom CoreGraphics menu bar renderers

Key implementation details

• Processes are enumerated via sysctl(KERN_PROC_UID) and enriched with proc_pidinfo(PROC_PIDTASKINFO) for CPU time and resident memory.
• CPU percentage is computed as a delta between consecutive samples, the same method Activity Monitor uses.
• The menu bar indicator is rendered to an NSImage using CoreGraphics, marked as a template image so it adapts to light and dark mode.
• The popover is managed through NSStatusItem and NSPopover rather than MenuBarExtra, which allows proper global hotkey integration and transient dismissal.
• Process grouping walks the parent PID chain with cycle detection, then falls back to bundle ID prefix matching for helpers that don't share a direct ancestry.
• The app runs as an LSUIElement (no Dock icon).

Requirements

• macOS 14.0+ (Sonoma)
• Not sandboxed. Reaper needs direct access to sysctl and proc_pidinfo to enumerate and inspect processes, which is not possible under App Sandbox. Distributed outside the Mac App Store.

License

MIT