I've not found a sequence that'll reproduce this consistently--it seems to happen in clusters, i.e., quiet and stable one day, then a crash every five or ten minutes the next. If I had to make a SWAG, I'd say it is triggered by dialogue and/or message notifications. If someone put a gun to my head for a really out-there SWAG, I'd say it seems more frequent after reloading, i.e., a game in progress, hit escape, load a previous save. Regardless, smells like a Unity defect; IIRC, 4.5 is in LTS so they should be willing to fix and/or backport fixes still.
Just have to let me know if I can provide any data or try out some repro steps.
Process: RimWorld725Mac [17967]
Path: /Applications/RimWorld725Mac.app/Contents/MacOS/RimWorld725Mac
Identifier: unity.Ludeon Studios.RimWorld
Version: Unity Player version 4.5.5f1 (4.5.5f1)
Code Type: X86-64 (Native)
Parent Process: ??? [1]
Responsible: RimWorld725Mac [17967]
User ID: 501
Date/Time: 2015-02-22 13:18:25.306 -0700
OS Version: Mac OS X 10.10.2 (14C109)
Report Version: 11
[...]
Time Awake Since Boot: 150000 seconds
Time Since Wake: 4700 seconds
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Exception Type: EXC_BAD_ACCESS (SIGABRT)
Exception Codes: KERN_INVALID_ADDRESS at 0x0000000204fed000
VM Regions Near 0x204fed000:
VM_ALLOCATE 000000018e8b5000-000000018e8b6000 [ 4K] rw-/rwx SM=ALI
-->
__TEXT 0000123400000000-00001234004f8000 [ 5088K] r-x/rwx SM=COW /System/Library/Extensions/AppleIntelHD5000GraphicsGLDriver.bundle/Contents/MacOS/AppleIntelHD5000GraphicsGLDriver
Application Specific Information:
abort() called
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 libsystem_kernel.dylib 0x00007fff8eee4286 __pthread_kill + 10
1 libsystem_c.dylib 0x00007fff9365eb53 abort + 129
2 libmono.0.dylib 0x000000010168ca05 mono_handle_native_sigsegv + 732
3 libmono.0.dylib 0x00000001016d4223 sigabrt_signal_handler + 100
4 libsystem_platform.dylib 0x00007fff8da5df1a _sigtramp + 26
5 libsystem_kernel.dylib 0x00007fff8eee4286 __pthread_kill + 10
6 libsystem_c.dylib 0x00007fff9365eb53 abort + 129
7 unity.Ludeon Studios.RimWorld 0x00000001003fbdc4 HandleSignal(int, __siginfo*, void*) + 36
8 libmono.0.dylib 0x00000001016d3e2e mono_chain_signal + 71
9 libmono.0.dylib 0x000000010162258b mono_sigsegv_signal_handler + 213
10 libsystem_platform.dylib 0x00007fff8da5df1a _sigtramp + 26
11 ??? 0x0000000204fed000 0 + 8673742848
12 ??? 0x00000001742c49c6 0 + 6244026822
13 ??? 0x0000000104afde1c 0 + 4373601820
14 ??? 0x0000000104afdb45 0 + 4373601093
15 ??? 0x0000000104afd9b5 0 + 4373600693
16 ??? 0x000000010a688cb8 0 + 4469591224
17 ??? 0x0000000110fa2f9f 0 + 4579798943
18 libmono.0.dylib 0x0000000101624228 mono_jit_runtime_invoke + 1788
19 libmono.0.dylib 0x0000000101746eab mono_runtime_invoke + 114
20 unity.Ludeon Studios.RimWorld 0x000000010040724f ScriptingInvocationNoArgs::Invoke(MonoException**) + 63
21 unity.Ludeon Studios.RimWorld 0x0000000100407209 ScriptingInvocationNoArgs::Invoke() + 25
22 unity.Ludeon Studios.RimWorld 0x00000001003f62ec MonoBehaviour::CallUpdateMethod(int) + 172
23 unity.Ludeon Studios.RimWorld 0x00000001002ec89d void BaseBehaviourManager::CommonUpdate<BehaviourManager>() + 269
24 unity.Ludeon Studios.RimWorld 0x00000001003ac468 PlayerLoop(bool, bool, IHookEvent*) + 1352
25 unity.Ludeon Studios.RimWorld 0x00000001006f4050 -[PlayerAppDelegate UpdatePlayer] + 240
26 com.apple.Foundation 0x00007fff96d16db3 __NSFireTimer + 95
27 com.apple.CoreFoundation 0x00007fff90ebfb64 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20
28 com.apple.CoreFoundation 0x00007fff90ebf7f3 __CFRunLoopDoTimer + 1059
29 com.apple.CoreFoundation 0x00007fff90f32dbd __CFRunLoopDoTimers + 301
30 com.apple.CoreFoundation 0x00007fff90e7c288 __CFRunLoopRun + 2024
31 com.apple.CoreFoundation 0x00007fff90e7b858 CFRunLoopRunSpecific + 296
32 com.apple.HIToolbox 0x00007fff8e481aef RunCurrentEventLoopInMode + 235
33 com.apple.HIToolbox 0x00007fff8e48186a ReceiveNextEventCommon + 431
34 com.apple.HIToolbox 0x00007fff8e4816ab _BlockUntilNextEventMatchingListInModeWithFilter + 71
35 com.apple.AppKit 0x00007fff8f0f3f81 _DPSNextEvent + 964
36 com.apple.AppKit 0x00007fff8f0f3730 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 194
37 com.apple.AppKit 0x00007fff8f0e7593 -[NSApplication run] + 594
38 com.apple.AppKit 0x00007fff8f0d2a14 NSApplicationMain + 1832
39 unity.Ludeon Studios.RimWorld 0x00000001006f3c17 PlayerMain(int, char const**) + 775
40 unity.Ludeon Studios.RimWorld 0x0000000100001b34 start + 52
[...]
Model: MacBookPro11,3, BootROM MBP112.0138.B14, 4 processors, Intel Core i7, 2.6 GHz, 16 GB, SMC 2.19f12
Graphics: Intel Iris Pro, Intel Iris Pro, Built-In
Graphics: NVIDIA GeForce GT 750M, NVIDIA GeForce GT 750M, PCIe, 2048 MB
Memory Module: BANK 0/DIMM0, 8 GB, DDR3, 1600 MHz, 0x02FE, -
Memory Module: BANK 1/DIMM0, 8 GB, DDR3, 1600 MHz, 0x02FE, -
AirPort: spairport_wireless_card_type_airport_extreme (0x14E4, 0x134), Broadcom BCM43xx 1.0 (7.15.159.13.12)
Bluetooth: Version 4.3.2f6 15235, 3 services, 27 devices, 1 incoming serial ports
Network Service: Wi-Fi, AirPort, en0
Serial ATA Device: APPLE SSD SM0512F, 500.28 GB
USB Device: USB3.0 Hub
USB Device: USB3.0 Hub
USB Device: Internal Memory Card Reader
USB Device: USB2.0 Hub
USB Device: USB2.0 Hub
USB Device: Audioengine D1
USB Device: Keyboard Hub
USB Device: Apple Keyboard
USB Device: BRCM20702 Hub
USB Device: Bluetooth USB Host Controller
USB Device: Apple Internal Keyboard / Trackpad
Thunderbolt Bus: MacBook Pro, Apple Inc., 17.1
Yeah, this is almost definitely a Unity/Mono thing. The call stack there doesn't even pass through any method I wrote (just some auto-included Unity code) so I'm afraid I can't fix this one. Sorry my friend :(